whats the bag that hangs on the side of the sump

[newfishliny]

I have seen more and more of these bags on the side of sumps with some sort of hanger device. whats the purpose and does the water from the over flow first go into it , then my sump or wet/dry.
I have a 90 with the back drilled out 2 over flows and 2 returns
thanks

 

[surfnturf]

It's a pre-filter

 

[smalltimer]

yep, get double of what your tank holds, the bags that is, wash in your washing machine the dirty ones, with small amount of bleach and HOT water, then in the rinse cycle add clorine remover.. then hang dry, I have 2 in my sump and 2 clean always ready to go, you will have crystal clear water and you will be amazed at how much junk these bags hold, make sure the water line is below the inlet of the bag or water will go over and not through the bag..

 

[newfishliny]

If I have a wet dry system , then where would I hang the bag,also I am installing a protein skimmer

 

[surfnturf]

It hangs under the incoming water from the tank(the water entering the sump), just screens out debris before it goes into the sump, simple, but effective.