I'm making a bait tank for herring today and I have a few questions on what I should do. I took a 144 quart cooler and rounded the ends off with sheet metal. In the little area at the corner behind the sheet metal, I have a 600gph bilge pump. Right now, I have a tube coming from the bilge pump through the sheet metal wall, When turned on this creates a good circular current all the way around the tank. I also have 2 aerator stones mounted in the middle of the tank on the bottom. Now here is my question.... I saw on the BOC where somebody used the bilge pump to pump water above the water level and then let it fall through a floating filter to remove ammonia, scales, etc. Would it be more benifical for me to use my bilge pump for current, or for filtration? I can't afford to get another bilge pump due to battery power constraints. Now, another option I am considering is filling the area behind the sheet metal up with charcoal or some sort of filtering stuff. When the bilge pump pulls in water, it'll pull the water through the filtering stuff. Thus, i'll get a good current flow, and some filtration. I really don't know if this would help any or not though, any thoughts you can give me would be greatly appreciated, thanks.