I don;t want to take over this thread but I do want to address some issues then call it a day. No, you can not ideally create the perfect ecologically sound environment in a closed system but you can come close. To do that means that you can't just over do everything. This brings up the practicality of fish keeping. If you need to do that much water changing to keep your fish healthy, that doesn't sound like a very practical way of fish keeping to me. How is one to enjoy this hobby with a job, family demands and whatnot when they have to be changing water 2 times a week to keep their fish from dying when just changing the setup to a more practical fish load to tank/ filtering set up will do this? As for the toilet issue, it congers up the image of unfiltered waste just sitting in the water polluting the water while in fact, the filtering system is supposed to be removing it out of the water so that it is NOT doing that. If your tank is full of fish "poo" maybe you need a better filtering system. But to bring this back to my retort, do you swim in lakes or the ocean? If you do, you are swimming in that toilet because the bottom of the lake and the ocean is loaded with fish "poo". If you don;t think so, think again. It takes time for that feces to decompose and get used so until it does, you are swimming in it. Lovely thought, isn't it? You want to compare that to your fish tank? As for your Discus tank, I don;t doubt that you can get away with that kind of set up IF you are using the right kind of water. Realizing that since ammonia is not in a toxic form at lower PH levels and bacterial life is altered and reduced thereby reducing the amount of eventual nitrates being produced, how can you say that that is a practical way for all tanks to be? It only applies when you have those water parameters. You need to mention that because it is NOT a general rule that applies to everyone. Also, if it is such a practical way of fish keeping, why aren't you doing it to all your tanks? I have too many tanks going for that to be practical for me and I'm sure most of the people in the hobby. Keep this in mind, water, is a vanishing commodity across the globe. The more we use up now, the less we have for tomorrow. Why promote a methodology that requires over use of it? My tanks are not pushed to the nitrate limits because I don;t over stock them. Therefore, there is no need to do massive water changes. I've had my water tested over the years at pet shops as well as the Rosensteil school for marine science at the University of Miami and none have found my levels to be anywhere near dangerous to sustain fish life. So this method I use has proven out multiple times over my 50 years of fish keeping. But the bottom line, I thought, was to advise people about fish keeping in ways that apply to all not just a few. And if it applies to a few, it needs to be noted so that people who are new to the hobby can understand that THIS or THAT may not apply to them should they come to a thread such as this. That's all I was sayin'