I don't really buy that the "system" is necessary. The zeo media provides a good medium for bacterial colonization, and I think the ability to release some into the system occasionally may be a reasonable way to add a food source. Exactly how big a benefit, if any is unclear; there is a reasonable theoretical reason to think it is beneficial, but whether or not that is the reason for their success isn't definitively shown IMO. Being that it's a form of carbon dosing, like any form of carbon dosing, it's quite effective at reducing N and P. And it does seem to be a very effective as far as carbon dosing goes. I tend to agree that some of the coloration stuff is likely bordering on "poisoning" the corals to get color though. This is discussed now and then in the chem forum if you look around. There is certainly a lot of evidence that many trace metals are poisons and it seems a lot of the coloration additives are such metals although they aren't always clear about the exact ingredients and concentrations. Used primarily for N and P reduction, it should be pretty safe, as long as you feed a decent amount.
