Tropical Fish Forums

[Flame Angel]

I have heard and read different arguements that the more coral there is in a reef tank, the better the water quality will be. The people who claim this say that the coral 'filters' all the tiny floating particles, and therefore making it cleaner. On the other hand, I'v heard that coral can make the water visually clearer, but not actually inprove the water quality as they produce wastes which had to the ammonia, nitites, nitrates ect. So what really happens?

[sirreal63]

What goes into a tank stays in a tank unless it is exported out. It may be converted into another form but it is still there. macroalgae absorb nutrients to grow but the nutrients are still there until you physically remove the macro algae. it will not be bio-available to other organism unless the algae dies but it is still there. A fish may eat the food you put in the system but that is converted and emerges as waste. The fish's body took part of the nutrients and the balance is excrement. It is all still there, nothing has exported it. So in short form the answer is the corals may uptake some nutrients but those nutrients are still in the system. Hard corals do not take in waste products but some soft ones do.

Most polyp feeding corals have restriction and a specified food and some of these are highly specific as to the size particle they can uptake. To make a blanket statement that they help purify the water is not accurate.
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[FloridaBoy]

FlameAngel, I'm not a coral expert but you pose an interesting question.
Corals come in many different types, but in general they are best thought of as carnivores; colonies of tiny anemone-like animals all constantly snaring/trapping food while also hosting symbiotic algae farms (zooxanthellae) in their tissues. But it has also been noted that some corals will actually absorb dissolved organics and bacteria into their membranes as food. Some authors indicate even trace amounts of ammonia and nitrates can be used by corals which is pretty interesting.

Corals are classified as "suspension feeders." They do remove suspended food like phytoplankton from the water, some of the largest polyps can even snare a small fish, however they do not filter or purify the water at the rate a clam will. For example, Tridacna clams are extremely efficient "filter feeders" and actually remove significant amounts of nitrate and ammonia from the water column. I have even read accounts of clam farms drip-dosing ammonium nitrate into their systems as clam food. So, maybe the next big leap in aquarium filtration will be... clams? Before you laugh--take a look at the last link below.

Mussels also move a lot of water, removing algae, plankton, toxins and silts; in effect purifying the water to a large degree. Even the problematic Zebra mussel does its part to filter the water. Here are a few links about how corals and also clams/mussels feed:

http://saltaquarium.about.com/cs/coralcare/a/aa021603.htm
http://saltaquarium.about.com/cs/coralcare/a/aa020803.htm
http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=1654&cid=123&search=
http://www.reefs.org/library/aquarium_net/0297/0297_6.html
http://www.pca.state.mn.us/kids/c-may98.html
http://www.spc.int/coastfish/News/Trochus/Trochus8/Trochus8-07.htm
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