Ah, I think I understand where the issue is coming from in this discussion. I may have misunderstood what the AmQuel was being used for.
I am referring to AmQuel being used as a dechlorinator. I only use the stuff when I'm doing water changes.
As Minnow said, AmQuel should not be used to replace water changes, because it's not actually removing anything from the tank. It makes the stuff less toxic, but "less toxic" does not mean "non-toxic." For that matter, even "non-toxic" doesn't mean it won't hurt fish given time.
The only way to safely avoid water changes is to find a way to actually remove nitrates from the tank (
zeolite, one of the "mega
nitrate-removing filters," or the Zero Water Change System(potentially), are the ways I can think of), and then only top the tank off with distilled,
RO, or rain water. Otherwise, stuff will build up in your tank and will eventually become dangerous to the fish.