Proper water circulation is one of many elements that are key to maintaining a healthy reef system. While there’s no such thing as a one-size-fits-all water-flow scheme (you really have to tailor the flow to the unique needs of the invertebrates you keep), there are certain signs that will tip you off to inadequate circulation. Among them:
1) Detritus buildup in “dead spots”
Some settling of detritus is unavoidable in a reef system, but excessive buildup tends to occur in tanks with inadequate water movement or “dead spots”—specific areas in the tank with poor to nonexistent flow. A good level of water movement will keep most particulate matter in suspension long enough to be captured by mechanical filtration media (socks, sponges, etc.), so this is a sign that you need to either boost the overall flow in the tank, by adding more or stronger sources (e.g. powerheads), or redirect existing water-flow sources to greater effect.
2) Corals fail to expand
When coral specimens remain in a prolonged contracted state—with their tissues/polyps withdrawn—one possible explanation is inadequate water movement. Now, many different environmental factors can cause this behavior, so failure to expand is by no means diagnostic, but that symptom coupled with others listed here may be a good indicator that better circulation is in order.
3) Leather corals have trouble shedding
Along very similar lines, if your livestock includes leather corals (e.g., Sarcophyton and Sinularia spp.), which occasionally go through a natural process of contracting their polyps, developing a waxy coating over their surface, and then eventually sloughing off this layer, inadequate water flow may make it difficult for them to shed. Or, they may go in and out of this cycle more frequently than seems normal.
4) Cyano shows up
Cyanobacteria, which tends to grow in loosely attached patches and mats, favors areas of slack water movement, so it’s appearance often indicates insufficient water flow overall or the presence of dead spots. Of course, cyano also favors elevated dissolved pollutant levels, so if it develops in your tank, you have more than one problem to remedy.
5) An “oil slick” on the surface
The buildup of an oily film on the water surface is a clear indicator of insufficient water movement. A little roiling action at the water surface (e.g., created by powerheads and/or sump returns positioned just below the surface) coupled with good protein skimming will help prevent this buildup while promoting good gas exchange in the system.
What symptoms have I missed?
What other signs and symptoms of inadequate reef system water flow can you think of? Please share them with your fellow salties in the comment section below.