I tried many things and ended up switching substrate.
Try looking for something you can cover the intake with which doesn't impede water flow, but I never found one...
Before the switch I tried many types of filters and spent soooo much money replacing them. It simply didn't seem worth it anymore.
If you decide to change like I did, remember to transfer the good bacteria by keeping some old substrate inside your tank (in a bucket which is fully submerged or something) and leave it there for a full week so the bacteria can begin to grow in your new substrate. I actually use a blend of gravel and rocks now and haven't had any problems. I kept the old sand in a circle and planted the plants in it, I then surrounded it by stones so that the fish couldn't get into the sandy area, this allowed me to keep a little bit of the substrate from the old in-place.