dude 2 Fx5's and korilla 4's are going to provide you with a LOT of flow for a fw tank, make sure your other fish can handle that kind of flow without stressing them. But asside from that if you angle yor power heads at the right angle you wont blow sand into the intake. I dont point them at the filter intakes, but in the same direction as my FX5 output to help boost it, and it gets most of the debris. What it dosent pick up collects in one of the pits my fish dig up and I just do like a 2-5g water change once it builds up enough to irritate me. Its super easy, fast and you remove the waste instead of filling your filter with it. Unless you have insano high reef flow your going to have some poo collect in dead spots over time.