everyody everything craps. there's no real "scale" however. Carnivorus fish will have more volume while livebearers and pleco's have the wonderful "coiled Charictor" Depending on the size of the fish too will weigh on how much the fish adds ferts to your tank.
And the more you feed em the more they poop too. Obviously. I do know however that for some reason Guppies tend to urinate in the water more than any other fish their size. Can't remember where I learnt that but it was many years ago.
How about little neons? I got 6 in addition to 2 platys and a gup. To me I'd say that about 3 neons = 1 platy or something in terms of waste, wouldn't it? (I'm just pulling this outta my coiled charictor )
Also, what can be done to lower the filter current into the water? The neons have to swim in hyper-drive mode to go past it.. It's actually quite funny to watch, but I feel bad for the little guys!
I'm also keeping up with with the water changes, religiously. But currently these guys are the tiniest neons ever.
You can either raise the water level, or if you filter has a flow control meter use that. My filter doesn't have a control meter, so I raise the inlet tube (the part of the filter that sucks up water) and that adjusts the flow. Since the tube sometimes falls back down, I had to think of a way to get it to stay. I take 2 strips of tape, both with the sticky side down, and put a little ball of paper between them. I then put this under the bent over portion of the inlet tube. This way the tube won't fall back down, increasing the flow. Anyway, that's my complex explanation of the day. ( And let me tell you, it wasn't easy) :
you could also put a sponge prefilter on the inlet tube.
I found that structure in the tank also blocks circulation creating dead spots. but some fish are built for speed. tapered fish like neons have a low surface area which equals less resistance which translates in to less effort to move thru the water. this in part is natures way of helping the small species like tetras survive . unless your filter is pumping several gallons per minute..the neons should be fine..if they are swimming in front of the outlet..it's becasue they want to.
I had danios that use to swim up the out flow on my AC whenever one was missing..I looked inside the filter and there they were swimming around.
danios are another fish built for speed.