I've been using the Fine grit black diamond blasting sand as a substrate in most of my tanks. I have a lot of problems with the outflow from my filters displacing the sand and causing craters in the substrate. Tank sizes of 5.5, 10, 20L, and 55 gallons. Anyone experience this or have any recommendations on how to reduce this without reducing the filter flow? I'm also wondering if capping the sand with the medium grit would help with this.