I have tried Quikcrete play sand and found it too fine... it would stick to the fish waste, get stirred up and was a general pain in the ass. I then tried Quikcrete all purpose sand, it was a good dark color but it took most of the day to wash enough for my 180g tank and it still took a long time to settle down in the tank. I thought the grains would be bigger too. Finally on a whim I went to a Namco pool supply store to see what they had, I had avoided pool sand because all the samples I had seen were to light in color... but what they had in stock was perfect. The color was much darker that what I had normally seen and it settles quickly so it does not get sucked into my filters.