Carissa;27971 said:Airstones are fine for non-co2 tanks that are small (like 20g or less). They help keep co2 levels stable in that type of environment, and provide some extra circulation in a tank with a very small water volume. But in a larger tank, or one that is co2 injected, a powerhead is a better idea.
guy tillmans;28591 said:i am probably mistaken, but heavy waterflow is only important in a hightech tank, when it's a low tech tank you don't need a powerhead.
CO2 is always in short supply in non-injected tanks, so any water movement that drives it out should be avoided. That includes any fixtures that cause a lot of surface agitation. Properly-sized airstones work fine in smaller tanks.
However, some water flow is needed in such environments to distribute nutrients. I use a small HOB filter which seems to do the job without a lot of surface disturbance; a small submersible pump, properly aimed, will work well as long as it didn't create a lot turbulence.