You may wish to add more oxygen to the water entering the filter shown in the post by Khoobg.


(Above drawing contributed by itdmraa)


(Above drawing for Filter Improvement by Mike S.)

This can be done by using a PVC "T" fitting on the input. The water would come in from the side of the "T" and a short section of pipe with a screen on top should be inserted into the top of the "T."
This is to keep the water from splashing out the top of what is now a "drop pipe." If the water is allowed to drop about one foot before it reaches the water level in the filter, there should be a good amount of extra oxygen for the bacteria in the filter to work with.

Mike Singleton
Spring Hill, FL
USA