Zoanthids do best under moderate, steady light, and new frags should always start lower and work their way up.
Most zoanthids are far more forgiving about light than stony corals, which is part of why they suit new reef keepers. They host symbiotic algae (zooxanthellae) that turn light into much of the energy the colony needs, but they can do that across a wide range of intensities. In practice, too much light too quickly kills more zoas than too little light does.
What PAR to aim for
PAR (photosynthetically active radiation) is the most useful number for placing corals. As a rough guide:
- Low light: about 30-50 PAR
- Medium light: about 50-150 PAR
- High light: above 150 PAR
Most Zoanthus morphs look their best somewhere between 50 and 150 PAR. Some established colonies will take more, but color often suffers above that. If you don't own a PAR meter, many local reef clubs lend them out. Measuring once at several heights in your tank takes the guesswork out of placement for years.
Acclimating a new frag
Frags often come from farms running lighting that is very different from yours. A safe routine:
- Place the frag on the sand bed or a low rock for the first week.
- Watch how the polyps open. Full, flat faces mean the light is comfortable.
- Move it up 2-4 inches (5-10 cm) at a time, waiting about a week between moves.
- Stop when color looks good and the polyps open fully most of the day.
If you've just changed fixtures or raised intensity across the tank, apply the same idea to the whole system. Drop the intensity by about a third and ramp it back up over three to four weeks.
Reading the colony
Zoanthids tell you fairly quickly when light is wrong.
- Polyps stretching tall on long stalks: reaching for more light. Move the frag higher, or raise intensity slowly.
- Polyps staying closed or opening only partly: often too much light, especially in the first days after a move.
- Faces turning pale, white, or translucent: bleaching. Lower the frag right away.
- Colors going brown or muddy: often an adjustment period, or a sign light was raised too fast. Give it two to three weeks, and lower the frag if it doesn't recover.
Spectrum and color
The neon look most people buy zoas for comes from fluorescent proteins that show up under blue and violet light. A blue-heavy LED schedule makes greens and oranges glow. A whiter spectrum shows truer, softer colors. Neither is wrong. Many keepers run a whiter midday peak and a longer blue period in the morning and evening so they get growth and color.
Photoperiod
A main lighting period of around 8 to 10 hours, with short ramps at each end, suits zoanthids well. Consistency matters more than the exact length. Avoid big jumps in schedule or intensity, and change one thing at a time so you can tell what caused a reaction.