Saltwater Inverts: Building a Clean-Up Crew for Your Perfect Reef

Saltwater inverts, short for saltwater invertebrates, include colourful snails, hermit crabs, shrimp, urchins, crabs, sea stars, and sponges. Invertebrates are animals without backbones. These creatures are the unsung heroes of the clean-up crew in both reef and fish-only saltwater aquariums. They eat algae (plant-like organisms that can cover surfaces), detritus (dead organic material), and leftover food. This process helps hobbyists maintain water quality and reduce the need for manual cleaning.

Adding saltwater inverts to your saltwater aquarium is a no-brainer. Not only do they provide practical benefits, such as cleaning up after your fish and enriching the tank's ecosystem, but they also have a fascinating history spanning millions of years. Snails, hermit crabs, and sponges each play a unique role in the tank's ecosystem, acting as small cogs in a well-oiled machine. The main question for hobbyists isn't whether to add a cleanup crew, but when the tank actually needs one and how many inverts to add for the tank's size. This article provides a practical guide to stocking saltwater inverts in home reef tanks and fish-only-with-live-rock systems ranging from about 10 to 180 gallons. Rather than cataloguing every species or discussing advanced breeding, we'll focus on the decision-making process that will help you build and adjust your invertebrate population to suit your specific setup.

Understanding Your Saltwater Inverts as a Clean-Up Crew

In the aquarium world, "saltwater invertebrates" is just a fancy term for any marine animals without a backbone that live in your tank: snails, hermit crabs, shrimp, crabs, urchins, sea stars, cucumbers, various types of worms (such as bristle worms and feather duster worms), and sponges, which are simple, filter-feeding animals. These inverts interact with the coral (the hard-skeleton-forming polyps), fish, macroalgae (large, visible algae), and microfauna (tiny, often microscopic animals) in your tank and, as part of the larger ecosystem, contribute to the balance and overall health of your aquarium. When you group them as a "clean-up crew," these diverse creatures share one thing in common: they eat organic waste, algae, and leftover food that would otherwise pile up and degrade your water quality.

These animals are a huge help to your reef tank or fish-only-with-live-rock system; they process the nutrients that would otherwise fuel those nasty algae blooms. Plus, inverts get around your tank on their own, reaching areas that your mechanical filtration and manual cleaning just can't get to, all 24/7. But understanding that not all inverts do the same job is key to building a crew that's really effective. So, it's super important to keep the number of inverts down to avoid overstocking and potential waste buildup. Keeping an eye out for healthy inverts, active movement, vibrant colouration, that sort of thing, will help you ensure that your crew is thriving. Most importantly, maintaining a balanced crew is crucial for overall tank health. The following sections will walk you through the specific roles and care of different inverts.

Functional Roles of the Clean-Up Crew Inverts

Clean-up crew inverts fall into a few functional categories, each targeting a different type of waste. We'll be looking at each of these roles in a bit more detail:

Algae grazers eat film algae, diatoms, and sometimes hair algae from rocks, glass and other hard surfaces. Think of snails like Trochus and Astrea, which are always busy methodically clearing every surface in the aquarium.

Detritivores and scavengers eat dead organic material, fish waste, and any leftover food. Nassarius snails are great at this; they burrow into the sand and shoot out to grab a bite whenever food hits the water. Crustaceans like hermit crabs roam around the rockwork, eating whatever they can find.

Sand sifters move through your sand bed, preventing it from compacting and eating any organic matter trapped down there. Fighting conchs are super at this role, and certain sea cucumbers do similar jobs, though cucumbers require a bit more experience to keep successfully.

Speciality pest controllers and filter feeders target specific nuisance organisms or help maintain water quality. Peppermint shrimp are a well-known example of pest control; they can munch on Aiptasia anemones. Emerald crabs can help control bubble algae, as long as they've got enough to eat, that is. And sponges, simple filter feeders that help keep the water clean and remove particulates, contribute to better tank health.

A balanced mix of these different roles will do a better job of keeping your tank clean than just adding a big batch of a single species. Your goal is to match the crew's capabilities to your tank's needs.

How Bioload and Tank Maturity Affect Invert Needs

"Bioload" is just a fancy term for the total waste production in your system, and it's determined by how many fish and corals you keep and how heavily you feed them. A lightly stocked 20-gallon nano reef, for example, produces a whole lot less waste than a heavily stocked 75-gallon mixed reef with a dozen fish getting multiple feedings a day. It's super important to keep your inverts in check, based on your tank size and bioload, to avoid overpopulation and keep the water quality up."

Tank Maturity": How Long Has Your System Been Running For?

Tank maturity is a term often heard in the aquarium world. It refers to how stable your system is and how long its biological processes have been running smoothly. Maintaining a stable tank is crucial for keeping invertebrates healthy, so ensuring this aspect is correct is essential. It's not just about balancing the nitrogen cycle and water parameters.

A mature tank develops a number of features over time, including established biofilms, stable bacteria populations, and even a consistent pattern of algae growth and detritus accumulation. Young tanks, even those that have just completed the nitrogen cycle, do not yet have these features. No matter how well you maintain it, a young tank will still look and feel quite different from a mature one.

So what does this look like in practice? Here's the typical progression of a tank over the first year or so:

Weeks 1–8 (cycling and early stability): Your tank's going through the nitrogen cycle, and you're just starting to see some stability creep in. Around weeks 2–4, you might start to notice a diatom bloom, that brown dust that forms on surfaces. There's not much in the way of food for your inverts to eat at this stage, so it's generally a good idea to hold off on adding them until you're sure it’s safe. Look out for signs like stable water parameters and the start of biofilm growth; that's when you know it’s time to bring in some inverts.

Months 2–12 (growth phase): By this point, your tank is really starting to kick into high gear: algae are growing, leftover fish food is piling up, and biofilms are developing on surfaces. Now that things are getting a bit more lively, it’s a good opportunity to add in some clean-up crew members, a few snails here and there to help with the detritus.

Months 12–18+ (maturation): At this stage, the tank is settling in, and clear patterns are emerging. Detritus begins to collect in certain areas, algae growth becomes more consistent, and you gain a better understanding of how quickly things break down and get cleaned up. Adjust the clean-up crew as needed to reflect the tank's readings.

By understanding these basics, you'll be able to determine exactly when your tank is ready for inverts and when you should wait a bit longer.

Deciding When Your Tank Needs a Clean-Up Crew

Rather than just following a hard-and-fast rule about how many snails to add per gallon, the key to success is paying close attention to your tank's individual needs. So how do you know when to add more clean-up crew, and when you're good to stand back and do nothing? The key is spotting the signs, things like a sudden diatom bloom or lots of uneaten food lingering around. By paying close attention to details, such as changes in algae growth, water clarity, and insect behaviour, you'll be able to make informed decisions about what your tank needs.

And of course, there's one golden rule: never overstock the tank. This is a recipe for disaster; it'll lead to a buildup of waste and potentially some pretty aggressive interactions between your inverts. Your tank will tell you what it needs to run smoothly; you just need to know how to listen.

Early Signs Your Tank Is Ready for Its First Inverts

Before you bring in any inverts, check these basic conditions; they're the minimum you need for a stable aquarium environment:

• You've had no ammonia or nitrite readings for at least a week or two, a good sign that your biological filtration is working properly.
• Nitrates are present but not getting out of hand. Generally, you're looking at under 30–40 ppm, which is a manageable level of nutrients.
• Your tank's been running with a standard photoperiod, day and night cycles, which is important for algae growth and other processes.

It's worth keeping a close eye on the details too, water clarity, algae patterns and all that sort of thing, because these are the things that'll give you a pretty good idea of how your tank is doing.

The one really reliable 'go' sign is that brown dusty coating that forms on everything as you get going, a diatom bloom. If you can spot this coating starting to form, that's generally a good time to introduce a small starter crew, a few snails and some Nassarius snails to keep things tidy in the sand bed. A decent rule of thumb for a 20–40 gallon tank might be 4–6 small algae snails and 2–3 Nassarius snails.

But do remember to hold back on some of the more delicate species, like sand-sifting stars, sea cucumbers and those decorative starfish (like Linckia), until your tank has had a bit longer to mature. These guys are sensitive to changes and need a stable system with a healthy population of microfauna to survive.

When Your Tank Needs More Clean-Up Crew

If you're starting to see some of these signs, like the glass needing scraping every day, green film algae everywhere, or food and detritus just piling up in the sand, that's a pretty clear indication that your current clean-up crew just can't keep up with things. Your tank's trying to tell you something; it's time to bring in some more inverts to help out.

Watch out for mulm and debris accumulating in the dead spots under rock structures; that's another sign your tank needs some extra help. Pay very close attention to the fine points of each sign in your tank; it's the tiny details that often reveal something's out of whack. For instance, if algae growth seems to occur only in a few specific areas of the tank, that could be a sign of a localised flow problem rather than too many invertebrates. Conversely, when you notice those signs alongside stable water parameters, it's probably time to bring in a small batch of inverts that target the specific problem you're seeing. Just be sure not to add too many at once and overwhelm the tank.

Warning Signs That You've Got Too Many Inverts

Overstocking clean-up crews is actually pretty common, usually because hobbyists follow outdated advice. You need to set a limit on the number of inverts you can have in your tank to maintain balance and avoid problems.

The following are signs that you've got too many inverts:

• Snails keep dying off one by one, even though the water parameters are rock solid and healthy. You might notice empty shells or just plain unexplained snail losses.
• Hermit crabs are constantly going at each other and killing snails just to get their shells or access some food. You might see a lot of aggression or just plain missing snails.
• The rock and glass surfaces of your tank look almost sterile, hardly any algae at all, yet your inverts are roaming around. The details here include observing really frantic searching or signs of malnutrition.
• You find yourself feeding your clean-up crew members by hand just to keep them alive. That tells you that you don't have enough natural food in the tank for them.

If you're seeing these problems, it's pretty clear your tank just isn't producing enough waste to support the number of inverts you've got in there. For example, a small tank with a dozen snails and a few hermit crabs can just as easily run out of algae and detritus in no time. What you need to do is rehome some of the excess animals; don't try to make up for it by hand-feeding them.

A Framework For Stocking Saltwater Inverts in Different Tanks

Here's a useful, adjustable framework for figuring out how many and what kinds of inverts you can add to your tank, based on its size and the number of animals you already have. This framework includes practical advice on checking the water, ensuring your tank is in good condition, and paying attention to how the parameters change when you introduce new inverts.

The main idea here is to start with a small number, and add inverts slowly, monitor the tank's response, and then make adjustments as needed.

Step-by-Step Method to Build Your Clean-Up Crew

Here's a simple process you can use every time you're setting up a new tank, restocking after some losses, or just rebalancing the existing crew:

1. Get a close-up look at your tank parameters and make sure everything is stable. Pay attention to all the details: make sure your nitrogen cycle is complete, that water parameters are stable, and that there's visible algae or waste that needs cleaning up.

2. Get a clear picture of your tank profile. Record all the important details, how big your tank is, what kind of tank it is (fish-only, softie reef, mixed reef, etc.), and what kind of animals you're planning to put in there (light, moderate, heavy bioload based on fish count and feeding schedule).

3. Choose the most important roles first. Use what you've observed in the tank, like film algae on the glass, detritus on the sand, or uneaten food in the crevices, to pick which types of inverts you need most.

4. Use some baseline ranges to decide how many inverts to start with. Always start at the low end, and remember you can always add more later, but it's much harder to remove excess inverts. Also, pay close attention to the details when matching species to your tank, and always keep your invertebrate population in check to prevent overpopulation and maintain balance.

5. Add new inverts in small batches. Put in new inverts a few at a time, every 2-3 weeks or so. Keep a close eye out for signs that the tank is either over-capacity or under-capacity before making each new addition.

6. Make fine adjustments. Instead of making big changes all at once, just add or rehome a few inverts at a time, and focus on keeping the ecosystem balanced over time.

Guidelines for Stocking Saltwater Inverts in Different Tanks

Here's a rough guide to help you get an idea of how many and what kinds of inverts you can add to your tank, based on its size and the number of animals you already have in there. These starting point ranges will give you a solid foundation for stocking your tank, but be sure to limit yourself to the lower end until you see how your tank stabilises. What these ranges are based on are just typical guidelines for tank setups, bioload, and the specific needs of saltwater inverts, so you'll want to adjust based on your specific aquascape: a dense rockwork needs more grazers, for example, or if you've got a bare-bottom tank, you may need fewer sand-stirring inverts.

10-15 gallon nano, light bioload

• You'll want to start with 2-3 small algae snails, like Trochus, Cerith, or Nerite, to keep things manageable.
• Add in 1-2 Nassarius snails to munch on leftover food and stir up that sand a bit.
• If you've got a small hermit crab or a single cleaner shrimp that'll get along with your fish, that's optional.

20-30 gallon, moderate bioload

• Mix it up with 4-6 algae snails that can cover different surfaces, like Trochus for rocks, Cerith for sand lines, or Astrea for glass.
• Get 3-4 Nassarius or similar detritivores to handle the extra cleanup.
• 1-3 small hermit crabs are a good start, and if you need some extra cleaning services, you can add in a peppermint or cleaner shrimp
• Hermit crabs and shrimp can be a great addition to a well-planned tank.

40-55 gallon, moderate to heavy bioload

• Get a diverse mix of algae snails, 8-12 to be exact, with Trochus, Astrea, and Cerith to cover all your bases.
• Nassarius or other sand-bed cleaners will be your go-to for 4-6 of them.
• 3-6 small to medium hermit crabs are a good number to aim for, and make sure you've got plenty of spare shells on hand
• If you've got an Aiptasia problem or need extra fish-cleaning services, that's where a peppermint or cleaner shrimp comes in.

75-120 gallon, heavy bioload mixed reef

• You're going to want 15-25 mixed algae snails to keep your rock, glass, and sand-line zones looking their best
• Nassarius or other detritivores will be your best friends for 6-10 of them.
• Don't be afraid to go big with 5-10 hermit crabs, just make sure you've got enough spare shells.
• Speciality inverters are a must for larger tanks, like conchs for sand maintenance or emerald crabs for bubble algae.

Surface area and aquascape complexity count just as much as tank size. A 75-gallon tank with a lot of live rock will need more grazers than a minimalist tank. Adjust your numbers accordingly and always keep an eye on how many inverts you can support.

Choosing Species Mix Based on Tank Goals

What you want to do is match your tank style to the right species mix. A coral-heavy nano reef is going to need smaller snails that won't mess up coral frags, for example. And if you've got a fish-only tank with big messy eaters, Nassarius and hermit crabs are your best bet; they can handle the extra detritus. A low-maintenance display tank just needs a few slower-growing grazers, and always keep an eye out for escape attempts.

Always check that the inverts you choose are compatible with your fish and coral. Some inverts are super sensitive to water conditions, so you'll want to keep an eye on those.

Advanced Considerations for Stocking and Managing Saltwater Inverts

Once you've got the basics down, there are a few other things to think about: making sure your inverts get along with your fish, keeping an eye on your tank's balance, not overpopulating, and adjusting your crew as your tank changes. Many of the popular aquarium fish you'd want to keep in your tank will go out of their way to eat the clean-up crew inverts you've so lovingly put in place. Triggers, puffers, wrasses and these big hawkfish are all notorious for seeing inverts as a meal rather than tankmates. You need to take a close look at the specific species of both fish and invertebrates you're planning to keep, and consider how their individual behaviours might affect your tank.

Before you go out and get a clean-up crew, do some research on the fish you're planning to keep and make sure they won't be eating your snails and shrimp for lunch. For example, if you've got a porcupine puffer in your tank, you're going to want to rely on urchins (those prickly buggers that fish don't dare eat), larger cucumbers and a good mechanical filter rather than snails and shrimp.

Coral care needs to be taken into account too:

• Large hermit crabs and urchins can be a real pain in the neck if they're knocking over or irritating your LPS or soft corals, especially if you've got some sloppy rockwork in your tank.
• Emerald crabs can get a bit peckish and nip at coral polyps if they're not getting enough to eat.
• Some peppermint shrimp from certain parts of the world have a bit of a taste for coral tissue, and while they might be great at eating Aiptasia, they're not so good for the corals.

Plan your rockwork carefully if you're keeping larger inverts like hermit crabs, and choose coral-safe species when building your clean-up crew for a coral-dominant system.

Manual Cleaning vs. Clean-Up Crew: Finding the Right Balance

Clean-up crews supplement, not replace, your basic aquarium maintenance routine. Water changes, filter cleaning, and the occasional detritus siphoning are still essential, no matter how many inverts you keep in your tank.

You've got a couple of options for cleanup crews, and each has its pros and cons. Here are the details to consider:

Heavy reliance on inverts: This is all about using inverts to clean the hard-to-reach areas in your tank, and with fewer glass scrapings and less need for manual detritus removal, it's not so bad. But you need to be careful not to overdo it and end up with a tank that's too crowded and a crew that's starving. Make sure you limit the number of inverts in your tank to avoid overpopulation and keep everything in balance.

More manual maintenance: This is the approach most people take: a smaller crew that focuses on specific areas of your tank, such as crevices in rockwork, underhangs, and sand beds where manual cleaning is difficult. You handle the glass scraping and detritus removal yourself, and the inverts focus on the hard-to-reach areas. This gives you a bit more control over nutrient export and lets you keep your tank in tip-top shape.

Most people find that a little bit of both approaches works best. Use your inverts to clean the areas you can't reach, and handle the visible detritus and glass scraping yourself as part of your regular maintenance routine. A reasonable expectation is that, with a properly sized clean-up crew, you should only need to scrape the glass once or twice a week, and detritus shouldn't build up in accessible areas between weekly maintenance sessions.

Adjusting Your Clean-Up Crew Over Time

As your tank matures, your needs will change, the fish will grow bigger and eat more, corals will expand and start blocking out the light that once hit algae-covered rock. Feeding schedules will get more complicated, and algae types will shift from diatoms to film algae to hair algae as your system matures.

You'll need to adjust your clean-up crew in response, pay close attention to water testing, tank conditions, and parameter monitoring, and make changes as needed to keep your tank healthy.

Adding inverts: As your bioload increases over time, you'll notice warning signs that you're not getting enough cleanup in your tank. That's when it's time to add some new animals to the crew. Aim for small batches of new inverts (3-5 snails, 1-2 hermits) every 3-6 months if you see these warning signs.

Rehoming excess: If you find you've got more inverts in your tank than you can feed, or that your hermit crabs have grown too big for your nano reef, it's time to limit your crew size by finding them new homes through local aquarium clubs or online forums.

Swapping species: As problems arise, you might need to swap out some of your inverts for new ones better suited to address the new issues in your tank. Bubble algae showing up? Get in an emerald crab. Is the sand bed getting brown patches? Get a fighting conch.

The key is to view your clean-up crew as a living, adjustable toolset that evolves with your tank, not something you buy once and forget about.

Common Clean-Up Crew Problems and How to Fix Them

Even with the best planning, problems will arise, so it's essential to pay attention to the details and diagnose issues in your saltwater invertebrate tank quickly and correctly. Understanding the most common issues and their solutions will help you respond quickly and avoid repeating the same mistakes.

Acclimation Shock: Marine invertebrates are much more fragile to large changes in water chemistry than fish. If you're moving an animal from a store tank to your own, and that store tank is running conditions that are way different to your tank, rapid transfer can be a killer. You'll often see lethargy or a lack of movement from an invertebrate as soon as you put it in its new tank. For example, snails may just freeze up and not move at all, or they'll even fall off whatever surface they were on.

Solution: Get to know the drip acclimation method and allow things to settle over 45-60 minutes, slowly matching the salinity in your tank to the store tank within a tiny margin of error, before you introduce your animals. Think a difference of less than 0.001-0.002 of a specific gravity at most.

Copper Poisoning: Copper is a serious problem for invertebrates; they can't tolerate the same levels as fish. Tap water that's been running through copper pipes, or residual copper from fish meds, this kind of thing can actually be a killer. Signs of copper poisoning in inverts are pretty clear, they stop moving, lose their colour, or suddenly you're seeing a lot of dead creatures all at once. For example, if all your hermit crabs or sponges just keel over in a short space of time, copper might be to blame.

Solution: Get a copper test done if you're using tap water, or if you've ever treated your tank with copper meds. If there's copper in the mix, switch to some RO/DI water pronto.

Starvation: Starvation is probably the most common reason you'll see your snails just dying off one by one over weeks or months. It's because there's just not enough food to go around. When you overstock your tank and the food gets eaten faster than it can regenerate, inverts start to get really hungry, and then they start dying off. The tell-tale sign is that over time, your inverts get less active and then start to disappear.

Solution: Sort your head out and reduce your inverted population. Don't add any more inverts until the algae and detritus in your tank build up visibly between cleanings.

Problem 2: Hermits Killing Snails and Each Other

When hermit crabs get hungry for a new shell, which happens pretty regularly as they grow, and there's not enough to go around, they'll either kill a snail to get to that shell, or they'll fight with each other. Pay attention to the details; it's really important to monitor the tank conditions and make sure there are enough shells for your hermits to choose from.

You might notice that the hermits are being aggressive, chasing other hermits or even attacking snails. For example, you might see a hermit crab forcibly removing a snail from its shell. This is a clear sign that there's a problem that needs to be sorted out.

Solution: Make sure your hermits have access to plenty of empty shells in different sizes. As they grow, they'll need bigger shells to get into. Check your shells regularly and chuck in some new ones to keep them all happy. If you've got a small tank, don't be afraid to reduce the number of hermits in there, or try a different species that's less aggressive. Scarlet reef hermits are generally more laid-back than blue-leg hermits, for example.

Problem 3: Algae Just Won't Budge

If you've got a big clean-up crew in there and you're still seeing algae problems, it's probably not the size of the crew that's the issue; it's what's going on behind the scenes. Take a closer look at your tank conditions. Are there any specific parameters that are off, or are you missing some basic testing procedures? Maybe there's a problem with the way you're feeding your inverts, or maybe there's a dead spot in the tank where detritus is building up.

Algae growth is fundamentally driven by excess nutrients in the water, too much or poorly balanced light, and insufficient tank circulation. If you've got a bunch of snails in your tank and they're still not making a dent in the algae, it's probably because you're not addressing the underlying issues. For example, if you notice that your tank has a thick layer of green hair algae on the rocks and the glass, despite having a big clean-up crew, that's a sign the problem isn't being fixed.

Solution: Get your nitrate and phosphate levels tested; if they're high, address them. Maybe it's time to reduce your feeding, run more water changes, or upgrade your filtration to address the problem before adding more inverts to the mix. Take a closer look at your lighting. Is it on for too long or too intensely? Maybe there are some dead spots in the tank where detritus is building up. Check your powerhead placement and see if you can adjust it to improve water flow.

Only add targeted grazers to address specific types of algae once you've sorted out the issues that are causing the problem in the first place. An urchin, for example, isn't going to solve a hair algae problem if you're pouring excess nutrients into the system every day.

Conclusion and Next Steps

Stocking a clean-up crew for your tank is all about listening to the tank's signals and being flexible; it's not about following some rigid "gallons-per-snail" formula that's designed to sell you more livestock. Your tank's bioload, surface area, age, and maintenance habits all determine how many inverts you need and which ones will work best for you.

Your next steps:

1. Have a close look at your tank today. What's the maturity level like? What's the algae situation like? And how much detritus is building up?

2. Work out how big your tank is and how much bioload it can handle, then compare that to the baseline ranges I've given you.

3. Plan a small initial batch of inverts targeted to the specific problems you're seeing; don't try to solve everything at once!

4. Keep an eye on things over the next 2-4 weeks and see what impact your cleanup crew is having.

5. Reassess your crew composition periodically as your tank matures and the bioload changes.

Some related topics worth checking out next include selecting reef-safe fish that won't eat your inverts, implementing long-term nutrient management strategies through refugia and protein skimming, and setting up effective quarantine and acclimation practices for your delicate marine invertebrates.

Additional Resources and Quick Reference

This section has some condensed references for stocking and observation; use it as a quick reference cheat sheet when planning additions or troubleshooting problems. For best results, pay attention to the details of each step and refer to images, if available, to help you spot the right species and healthy behaviours.

Typical timeline for adding a clean-up crew to a new tank:

• Weeks 3-4: Your first small batch of hardy snails, like Trochus and Cerith, can be introduced as soon as ammonia and nitrite are zero and diatoms appear. And by the way, Trochus snails are great at munching on algae.
• Weeks 6-10: You can then expand your crew by introducing some more snails. Nassarius are good for the sand, and if you want to, get some hermit crabs in at this stage.
• Months 3-6: It's around this time you can add the more specialist inverts, whatever your system needs, like emerald crabs or conchs, urchins, for example
• Months 6-12+: Only when you have a semi-mature and stable system, then you might want to consider getting in some of the more delicate creatures like sea stars or cucumbers

Signs that you've got an understocked team:

• Every day, you're having to scrape away at the glass.
• Detritus is just piling up in the low-flow areas.
• That green algae is going to be all over the rocks between cleanings.

On the other hand, signs that you've got too many inverts:

• Snails are slowly dying despite good water quality.
• Hermits and snails are at war, so you find snails dead and hermits alive.
• The inverts are all on the move all the time, with nothing much to eat.
• Even though you’ve got plenty of food floating around, you end up having to feed them separate bits because they’re starving.

What to look for when buying inverts- pay attention to the details:

• If it gets touched, it moves or retracts: that's a good sign.
• Shells should be intact with no chips or cracks.
• No visible signs of parasites or unusual growths
• Shrimp and crabs have all their bits.
• Try to avoid any animals that have been in the shop for less than 48 hours, and, as a rule of thumb, a healthy hermit crab will scurry for cover when disturbed.
• Keeping a simple log of what inverts you've added and how they do over time can really help you fine-tune your system. Every tank is unique, so it's worth recording all the changes, what you add, when you add it, and how each animal fares.

For more on inverts care and keeping your aquarium thriving, you can also sign up for our newsletter or channel for the latest advice and tips on keeping saltwater inverts.