Blackworms ALIVE in my Filter??

[discusnovice]

I cleaned my Magnum 350 yesterday and discovered a number of CBW's alive in my canister. Does this present any kind of a problem. I have been feeding CBW for at least 6 weeks now and this is probably the first time the canister has been cleaned since I installed it 3 or 4 weeks ago. Your thought on these worms living in my filter and my pea gravel substrate with reverse flow.

[Carol_Roberts]

I bet you can guess my thoughts ;)
Prefilter sponge on the water intake to keep cbw OUT of the filter. . . . . and the gravel . . . well, that's why I don't have any in my discus tanks. . . .