noticed several months ago when I cleaned out my Fluval some little white bugs (1/2 a pin head size)...population has increased to billions. Seem to come out at night and disapear into the gravel by day (most of them). 8 mature discus plus tankmates in a 90 gal planted aquarium. Occassionally notice a bug or two on the fish but mostly on the wood, plants and glass. How do I get rid of them? Any natural preditors?