powerhead feeding too much air?

[fluffer]

Can you use a pump rated up to 50 gallon in a 20 gallon tank? I just put a zoo-med 226 powerhead in my tank. This morning my damsel was fine before I put it in. I installed it during my lunch, and when I came home from work my fish was breathing heavily and floating kinda sideways. I tested chemical levels, and everything is fine, and I have the pump set on the lowest flow level. Oh, and he still ate dinner (slowly though). Is there any way to restrict the airflow to a safe level, or do I have to switch it out with a lower flow model? Please help:confused:

[OrionGirl]

Where is the air coming from? You can close off the air intake for most powerheads--which I recommend. Bubbles increase evaporation and salt creep.

[fluffer]

It's a venturi hose from the top of the head. Can I pull out the hose and suck in water through the hole? Or should I leave the hose on, and put a little piece of plastic over it? Thanks

[DEmigh]

All of the powerheads that I own have a small plug that can be placed in the venturi hole to prevent water intake. I imagine the suction would present a minor hazard to small/weak-swimming fish. Taping the end of the tube should do the trick.

[fluffer]

Thanks guys. I covered the air inlet, now my fish is better and loves the extra current. He's more lively than ever!