Hi all im realatively new to this forum & would like some advice on how to get rid of water fleas my sump tank has become infested with them as has the media/bio balls & i dont want them getting into the main tank,i keep mostly malawi,s along with the odd oddball, the sump is a secondary filter used as a biological system along with a fluval fx 5 as mecanical i intend to increase the flow rate on my sump as at them moment it is only about 5/600 litres an hour,any help would be appreciated Steve

Why do you not want them in the main tank? They would be a great live food for your fish if they can find their way into the main tank. You would also see more activity with your fish as they would be eagerly searching for them as an extra tasty snack.

Sounds like Copepods? no harm in them and fish will pick them off.
Any pics?