Do you need this if you have that?

[captmicha]

You don't have to, you just need to keep up with water changes and either lightly stock, or plant heavily. Air powered filtration is very economical but it has its limits, it needs you and plants to help it out.

They're heavily planted but not as much as I'd like b/c I can't afford/don't have the energy to keep up with CO2. And I also don't have the energy to keep up with frequent enough tank changes. I might be able to soon but not now. I tried being responsible and finding homes for some of my fish but most wanted to put them in goldfish bowls and I started not being able to trust anyone to take them.

Generally speaking, tanks with slender fish with little biomass will do fine on just sponge filters.

I wouldn't say it's an all or nothing situation. What kind of tanks are you running right now?

All are planted, except for my snail tank. 2 are 10 gallon guppy tanks, a 2.5 gallon fry grow out tank (platy and guppies), 3 gallon with two peacock gudgeons and huge brown algae problems, a 15 gallon with varied fish, a 5 gallon with shrimp and a 5 gallon, unplanted, with snails.

 

[platytudes]

These definitely sound like they could do fine with air powered filtration alone, except maybe the 15 gallon tank. Why don't you start out with just a couple of tanks? Go for the Swiss Tropicals filters like MsJinkzd uses, those are the best...the Poret foam is exceptional compared to most others. There are plenty of cheap sponge filters, like the XY kind from eBay, but the extra you pay for the high quality ones is well worth the money.

If you can't do water changes as often as you would like to, Tetra Easy Balance does really work to reduce nitrate. Many poopoo it, but it does exactly what it claims to do - binds nitrates. It isn't as good as water changes, it's true (water changes remove a lot more than nitrate) but it does work to keep nitrates low, which is the source of many problems such as algae.