I based my idea of internal filters from looking at online stores. Yesterday I took a good look at them in a store. I was not impressed. For the size there really isn't much filter media in them. They take up to much space for the small amount of filtering they do.
I am starting to look at the simple sponge filter used with a small powerhead. A piece of plastic riser tubing, cut and shape a piece of foam and a powerhead. Guess this has turned into a DIY
For now I replaced the plastic screen on the bottom of my powerfilter tube with a piece of coarse foam. This will act as a prefilter and a place for bacteria to grow. So in the powerfilter I cut out the blue coarse fiber filter media from the cartridge and replaced it with the finer white polyfiber. Put the filter in a net bag to hold it all together.
Just overnight I could tell the water was clearer. The bonus is never having to buy a filter cartridge again. Less than a dollar for the foam, $1.50 for a net bag and $2.50 for a bag of polyfiber that will last a very long time. A cheap way to upgrade most powerfilters.