It should help because it will remove organic matter (fish waste, excess food) which causes amonia then nitrite then nitrate. By external do you mean hang on back or sit next to your sump in the stand. For next to the sump if your looking for a good skimmer get the aquaC ev 120. They run using a magdrive 5 which can be mounted external. If you want a hang on back I like the turbofloator multi. It gets a pretty good dry foam. Some people use the aquac remora but I particulary don't care for them, they are about as good as a cpr bak pak but more exspensive.