Kevin, focus on the big picture. As long as the fish waste is not ended up at the bottom of the grow bed, you win.
As for the sand, I am testing the Play Sand I purchased from Rona (I live in Canada).
Yes, maybe this type of sand is too fine but I still have hydroton and simply place hydroton at the bottom and then add my sand. Just in the testing stage so that I do not need to follow every detail of iAVS, otherwise you will never be able to start.
BTW, I have not placed any fish yet so that I can add whatever I want to test. For example, I added a whole 4L milk bottle of fermented urine to the sand to see how clear the water be coming out of the grow bed. Well, the result? Clear water.