Yup. Not doing water changes, regardless of whether you have a refugium or not is, IMO, a bad idea. People are focused on what they can test for, but there are many many many things that accumulate (or are depleted) through time that we don't have a thought to test for - nor understand the implications. IMO, it is like not cleaning an animals cage. If can survive, but it may lead to disease. It still gets air, but it sure may smell a whole lot.
I've been looking more deeply into the Ecosystem thing. Seems to have a fantastic marketing strategy, IMO. Its all a "miracle." Don't ask questions, and that makes me real uneasy like. Works on freshwater, saltwater, reef tanks...they sell an additive that makes "miraculous" claims (cures HLLE) and yet I can't find a mention of what it contains except NOT to use the FO one in a reef tank. :notsure: I agree it is best to do water changes with ecosystem filters just like you would with the poor man's equivalent refugium. That's a wise choice. :yes: There are very few couple of hundred gallon (being generous) self sustaining marine ecosystems that get no outside input in nature. Ecosystem filters work great, no doubt about it, which is why people came up with a way to turn a rubbermade container into basically the same thing, LOL
Success motivates knock offs
Which is why I seriously considered trying to make a knock off skimmer out of some rubbermaid containers and a few fittings....