Colorful zoanthid coral polyps in a row on a dark background

Water Flow

Moderate, indirect flow keeps zoanthids clean and open without pinning their polyps shut.

Zoanthids grow as flat mats of short polyps, and that shape catches debris. Fish waste, uneaten food, and detritus settle between the polyps and smother the colony from underneath. Good flow is mostly about keeping that from happening. Ideally it shouldn't hit the polyps hard enough to keep them closed.

What "moderate" looks like

There is no single gallons-per-hour figure that works for every tank, so judge flow by what the colony does.

  • Right: polyps fully open, skirts swaying gently, no debris collecting on the mat.
  • Too strong: polyps half closed, faces folded or bent over, tissue peeling at the edges of the colony.
  • Too weak: fine debris or a film of algae settling on the faces and between the polyps.

Random or alternating flow from a wavemaker is better than a steady jet from one direction. Changing flow cleans the colony from several angles and keeps one side from being battered all day.

Placement tips

  1. Don't aim a pump straight at a zoa colony. Let flow bounce off glass or rock first.
  2. Avoid dead spots behind rockwork, where detritus collects.
  3. Put new frags where flow is gentler for the first week while the base attaches.
  4. Watch for flow changes as other corals grow. A spreading leather coral or SPS colony can create a dead zone where there wasn't one.

Manual cleaning

Even in well-planned tanks, a quick manual cleaning helps.

  • Once or twice a week, use a turkey baster to puff water across established colonies.
  • Use just enough force for the polyps to close briefly, then move on.
  • Skip this on newly glued frags until they are firmly attached, or you may blow them off the plug.

This is also a good chance to check for pests. Basting often shakes loose nudibranchs, snails, and sea spiders hiding at the base of polyps.

Flow and feeding

If you feed your zoas, turn the return and powerheads off or down for about 10 minutes so the food settles on the polyps instead of blowing past. Most controllers have a feed mode for this. Remember to check that pumps come back on afterward.

Signs flow has changed

Pumps slow down as they get dirty. If a colony that used to look clean starts collecting debris, clean the impellers and check flow before blaming lighting or water chemistry. Periodic pump maintenance, every few months for most wavemakers, keeps flow predictable.