Any slow current filters?

I'm in the process of dealing with a BGA outbreak in my low tech 20 gallon long tank(that's what I get for leaving lazy friends in charge of my tanks while I'm out of town for a month). I know what I have to do to deal with it (both corrective and to prevent future outbreaks), but I'm also thinking, for the time being, I should probably also get a filter going with some media from my 10 gallon to help out until the tank's good bacterial load and surviving plants are re-established. The problem is that the fish in the tank(Boraras Merah) prefer sluggish water, so I need to find a filter that will not create too much movement. Can anybody recommend any filters that might work? I would prefer any that are not Hang on Back types, just a preference on my part as they've been nothing but trouble in the past for me.