I love the sand substrate in my tank but im losing my patients rather rapidly, everytime I do a water change and suck up any debris on the sand the next day its back to square one

not only that but today I have noticed brown algae on my thermometer and my SNAIL. I do my water changes reguarly so why is this happening, is it the plants? I'm not even sure what the crap on the bottom of the tank is, no fish could possibly poop as much as that surely and I don't feed my fish too much so its not food. My corys don't seem to be helping either.
Other than water changes is there anything else I can do, I don't want to be adding anymore chemicals to the water as I already add Aquasafe and plantamin. I am so stressed out, all I want is a nice looking tank lol.