Why does my Gamma Knife Hydnophora Coral develop dead patches on shaded undersides?

Hydnophora rigida self-shades as it builds steep ridges. In lower flow and light, the shaded base can starve, leading to STN from the underside. Mount it high with open space around the colony and provide strong, turbulent flow. Rotate or reposition frags early to expose new faces; once thick, trimming overhangs may be needed.

How aggressive is it, and what spacing prevents stings?

Hydnophora has very potent nematocysts and will send short sweepers and mesenterial filaments that can burn neighbors within 2–4 inches, sometimes more in high flow. Give 4–6 inches of clearance from Montipora, Pocillopora, and fleshy LPS. Avoid downcurrent placement toward sensitive corals, and use rock “moats” to block contact.

My neon green turned dull or brown. Is this nutrient or light related?

Both can drive color shifts. Sudden high PAR can bleach tips; ultra-low nutrients can wash out fluorescence; excess nutrients deepen brown zoox. Target moderate–high PAR (200–300) with acclimation, random high flow, and stable alkalinity. Aim for low but present nutrients (nitrate ~2–10 ppm, phosphate ~0.02–0.08) to keep vivid greens without browning.

What’s the safest way to frag Hydnophora rigida without causing rapid tissue loss?

Use a diamond saw or sharp bone cutters to make clean cuts between ridge valleys; avoid crushing the skeletal ridges. Dip in an iodine-based solution, then place frags in high, turbulent flow to keep cuts clean. Maintain very stable alkalinity and temperature for a week; epoxy only the base to prevent smothering living tissue.

TSA Gamma Knife Hydnophora Coral

Beginner Corals LPS

Overview

Gamma Knife Hydnophora Coral forms thick, ridged branches with sharp, tooth-like protrusions. Hydnophora rigida is a stony branching coral that prefers moderate to high light and strong, turbulent water flow. It is photosynthetic through symbiotic algae but also accepts small meaty foods, which can support growth and maintain color. Place with ample space and avoid contact with neighbors, as its sweeper tentacles and tissue can damage nearby corals.

Quick Facts

Care Moderate

Lighting Moderate–High

Flow Moderate–High

Placement Mid–High

Temperament Aggressive (6–8 inches spacing)

Recommended Parameters

Temp 75–80°F

pH 8.1–8.4

Salinity 1.025–1.026

Calcium 420–450 ppm

AlkAlkalinity 8–9 dKH

Magnesium 1250–1350 ppm

Feeding photosynthetic (primary), microplankton, zooplankton, rotifers, cyclops, finely minced mysis shrimp, brine shrimp nauplii, coral-specific powdered foods

Care & Placement

Gamma Knife Hydnophora Coral (Hydnophora rigida) thrives with stable, SPS-like conditions and space to prevent stings to neighbors. Provide strong, stable lighting at ~200–300 PAR and high, random flow to keep tissue clean and prevent detritus buildup around the hydnophores. Place mid to high on rockwork with at least 6–8 inches (15–20 cm) clearance from other corals; this species is very aggressive and can send out sweeper tentacles, especially at night. Target feed is optional; it is primarily photosynthetic but accepts fine particulate foods (e.g., rotifers, reef powders) once or twice weekly, which can support growth and color. Keep temperature 24–26°C (75–79°F), salinity 1.025–1.026, pH 8.1–8.4, alkalinity 8.0–9.5 dKH, calcium 400–450 ppm, magnesium 1250–1350 ppm, nitrate 2–10 ppm, phosphate 0.02–0.08 ppm. Monitor with reliable test kits and a refractometer; this coral is sensitive to rapid swings, especially in alkalinity and salinity.Acclimate by dipping, then light acclimating over 1–2 weeks (use a screen or start lower and raise). Mount securely to handle strong flow. If tissue pales or bleaches, reduce light intensity or raise the coral and increase nutrients slightly; if tissue recedes (STN/RTN), stabilize alkalinity and temperature, improve flow, and consider fragging healthy areas. Avoid shading from faster growers and keep pests and algae off the base. Run activated carbon if mixing with soft corals to reduce chemical stress. Regular small water changes and a dosing plan for alkalinity, calcium, and magnesium help maintain the stability this coral needs to grow and keep sharp-looking ridges.

FAQ

Frequently Asked Questions

About the TSA Gamma Knife Hydnophora Coral

Why does my Gamma Knife Hydnophora Coral develop dead patches on shaded undersides?

Hydnophora rigida self-shades as it builds steep ridges. In lower flow and light, the shaded base can starve, leading to STN from the underside. Mount it high with open space around the colony and provide strong, turbulent flow. Rotate or reposition frags early to expose new faces; once thick, trimming overhangs may be needed.
How aggressive is it, and what spacing prevents stings?

Hydnophora has very potent nematocysts and will send short sweepers and mesenterial filaments that can burn neighbors within 2–4 inches, sometimes more in high flow. Give 4–6 inches of clearance from Montipora, Pocillopora, and fleshy LPS. Avoid downcurrent placement toward sensitive corals, and use rock “moats” to block contact.
My neon green turned dull or brown. Is this nutrient or light related?

Both can drive color shifts. Sudden high PAR can bleach tips; ultra-low nutrients can wash out fluorescence; excess nutrients deepen brown zoox. Target moderate–high PAR (200–300) with acclimation, random high flow, and stable alkalinity. Aim for low but present nutrients (nitrate ~2–10 ppm, phosphate ~0.02–0.08) to keep vivid greens without browning.
What’s the safest way to frag Hydnophora rigida without causing rapid tissue loss?

Use a diamond saw or sharp bone cutters to make clean cuts between ridge valleys; avoid crushing the skeletal ridges. Dip in an iodine-based solution, then place frags in high, turbulent flow to keep cuts clean. Maintain very stable alkalinity and temperature for a week; epoxy only the base to prevent smothering living tissue.