Sounds like maintainence is fine then and your problem is just the aeration.
To keep the balas you're looking at a tank over a hundred gallons, plus they need to be kept in a school, you'll be better off rehoming them while they're small to avoid stunting them.
Puffers don't do well with any other fish as they're vicious little buggers... even if they do well for a short period of time, they can snap overnight and rip tankmates in half. You could do a small species tank with a single dwarf puffer (5 gallons would actually be enough for one) and no other fish. If you end up keeping the puffer, another thing to keep in mind is he'll need small snails in his diet to trim down his beak.
Is this what your buttefly loach looks like? He should be fine in your tank. If you want a pleco that doesn't eat plants you could go for one of the varieties that prefer wood (like the clown pleco) or meaty foods.
Planet Catfish has great information on lots of species, sizes and diets.
There are a few smaller loach species like the zebra loach that make great bottom dwellers, or you could keep some corydoras catfish. Both need to be kept in groups of at least three, preferably more. Tetras are great, but you'll also want to keep those in groups, maybe get a few more cardinals? Don't get anything with long fins as your barbs will nip at them.
