20 gal
tetras - von rio, neon, rummy nose, black neon; otos, guppies
sponge via powerhead
just added rummies, likely needed to do another water change due to that
no idea, been about a year or two
flakes
a pinch a day
none on purpose, but theyre impossible to get rid of and do help keep things clean
How many of each? Seems to me like your aquarium is a tad overstocked