30–100 gallon aquariums: choosing a mid-size reef tank
The 30–100 gallon range covers the reef tank sizes most hobbyists actually build: 40, 50, 75, 90, and 100 gallon systems. These tanks hold enough water to keep temperature and chemistry stable, have room for a real community of fish and a mixed reef, and still fit in a living room, office, or bedroom without special planning. We carry mid-size systems from Red Sea, Innovative Marine, Nyos, and UNS, from all-in-one tanks to sump-based reef systems.
30–50 gallons: compact reef systems
A tank this size is a big step up in stability from a nano. The Innovative Marine NUVO Fusion Pro 2 40 is an all-in-one aquarium with its filtration built into a rear chamber, and the Red Sea REEFER 200 G3+ pairs a 41.7-gallon display with an 11.1-gallon sump for 52.8 gallons in total, on a 23.6" × 22.6" footprint that fits where a longer tank won’t. It is a great range for a first reef, a clownfish pair with a few small community fish, and soft corals and LPS.
50–80 gallons: room for a mixed reef
The middle of the range is where most mixed reefs live. The Red Sea REEFER 300 G3+ has a 65-gallon display measuring 35.4" × 22.6" × 21.7" over a 14.3-gallon sump, and the REEF-FRAME 350 offers a 74.6-gallon display on a 4-foot footprint. These tanks have room for a broader fish list, more aquascaping options, and stony corals once the system is stable. Shallow designs like the Innovative Marine NUVO SR60 put corals closer to the light and are easy to reach into.
80–100 gallons: the top of the range
At the upper end, the Nyos OPUS G2 440 holds 100 gallons in a sump-based system, the Innovative Marine NUVO SR80 is a full-size shallow reef all-in-one, and the UNS Reef System R80 uses a center overflow for 360° circulation and includes frag trays for coral propagation. Tanks this size carry heavier fish stocking and larger coral colonies, and a filled 100 gallon system can weigh more than 1,000 pounds, so plan the location before you order.
Equipment to plan for
Most reef-ready systems list both display and total volume, and the difference matters when you shop for equipment: size lighting and flow to the display, and size filtration and heating to the total.
- Lighting: a 2-foot tank can usually run one reef light, while 3- and 4-foot tanks typically need two fixtures for even coverage. Compare options in aquarium lighting.
- Flow: run two powerheads on opposite sides or ends of the tank so there are no dead spots behind the rockwork.
- Filtration: on a sump-based system, size the protein skimmer and return pump for the total system volume and the head height your plumbing runs.
- Automation: an auto top-off keeps salinity steady as water evaporates, and an aquarium controller can monitor temperature and pH.
Stocking a 30–100 gallon reef
Start with hardy community fish such as clownfish, gobies, blennies, and cardinalfish, and see beginner saltwater fish for more ideas. Tanks from 75 to 100 gallons can also take more active swimmers such as wrasses and anthias. Most tangs and larger angelfish need more swimming room, so look at our 101–150 gallon aquariums if they are on your list. For corals, beginner corals are a good place to start.
Related aquarium collections
Need something smaller? Browse nano aquariums. You can also compare all-in-one aquariums across every size or shop all aquariums.
