fluval 4plus filter not filtering properly

[buddy]

I have a Fluval 4 plus and a 3 plus filter in a 120 gallon tank for my turtles (I only fill it with about 60-70 gallons) and when I changed the filter the sponge was only 1/3 used and dirty, the rest of the filter was still clean. The red button was up and showing that it was needing to be cleaned, also my aquarium was not staying as clean as usual. Any ideas about whats going on with my filter?

 

[mfdrookie516]

You might want to go through the whole filter and clean everything out real good. I dislike internal filters for this reason. They can get clogged up inside and not do a very good job, but its hard to tell until you actually start taking them apart. Clean out the impeller real good, and anywhere else you get get a small brush.