It could be that the powerhead is too powerful for your desired flow and/or tank configuration. If your 25 is as high as it's deep/wide, there is very little distance for the flow to travel, so that powerhead might indeed, create too much surface turbulance for your set-up.

It's not the gallon capacity so much as the surface area and each powerhead mfg's particular design, so you may have to try more than one model to get just the surface action you want.

Does it have a diffuser to spread out the water flow? Maybe a tall piece of driftwood can block the flow. Also use the airator tube to add air [=less water].

If you are using it for a UGF then you can reverse the flow and change the direction which will definately slow it down to more of what you need. You can also use the venturi or air tube which will slow it down a bit. In addition to driftwood, filter foam would diffuse it good. Another way is to position it pointing towards the side or back of the tank. You may have to back it up a few inches so not to create too much surface agitation.