Well A pleco clean the bottom of my tank ?

[GodFan]

Sorry.....
Um yea water changes are the way to go. I would get natural color gravel substrate and then live plants. I know oscars eat most but there are a fee he will not I believe. Worst case scenario run a piece of pvc pipe down one corner into the substrate and put pothos vine in it. The roots will eventually work through the substrate and "eat" some of the poop.

 

[Goldfish loach boy]

Really the only thing that ears poop, are plants, nothing else does. Nothing will get nutrients from poop, of you see a fish trying to eat poop, you are under feeding
On a side note guys, just FYI, a lot of animals eat poop and poop it back out to extract all the minerals they can from their food/ waste, this is called coprophagy