Hello

I have a small aquarium which have a Hailea HL-BT200 filter and have the airstone at the same time. How much air would be good? It have a small air regulator but it don't regulate well. It's all the same rate. Should I buy an air regulator?

An Air regulator is always goout if you d to have, depending on the fish you are keeping and your esthetic preferences normally I like a very slow air rate in the tank but if you have a heavy bio load then you might need a higher flow to oxygenate the water.

But if it is too much will it do any harm?

it will annoy the fish and stress them if it's too much, you will be able to tell from the behavior of the fish.

What is the behaviour they wil be doing if they are stressed or annoyed?

If the flow is too strong the fish will be swimming erratically and trying to avoid the worst affected areas. It should be quite obvious if you see such behaviour.

Joseph

What type of setup should I use? Because it can be used 2 diferent setups. 1 is direct flow from the filter and an airstone altogether or the other one is it can be on top of the aquarium like a rain fall. Which one is best?

Actually both are OK so long as the flow itself is not excessive. It's up to you really. There's no better or worse as such in this case.

Joseph

Well said hammerhead, it's up to personal preference I like the rain fall type as it resembles nature more but I've seen setups which looked really nice with the airstone effect.