Pool filter sand. Wont kick up like play sand when disturbed and only requires one rinse and shouldnt have any debris in it, play sand definitely requires a bunch of rinses and will cloud the tank until it settles unlike pool filter sand. Personally i dont like the color of pool filter sand but thats me, i use black diamond blasting sand which is black i rinsed it once dropped it in and its been great since, its inert doesnt kick up dust when disturbed and perfectly anchors my plants. I have a bolivian Ram in the tank and he sifts through the sand no problems, posters will warn you against using blasting and pool filter sands as they are considered " industrial" sands but quikrete is also an " industrial" sand. Ive used play sand pool filter sand and blasting sand, they are all similar in price, PFS will have the largest grain size of the 3 play sand will be the messiest of the 3 and blasting sand will be the one people are most scared to try. Blasting sand comes in 3 grit sizes the fine grit is most like play sand or the fine sand one would find in eco complete or tahitian moon sand, medium grit is a bit smaller than PFS but not as fine as play sand and the bigger grit which i wouldnt recommend is bigger grain than PFS. With all 3 i dont think one can go wrong just depends on what one prefers i guess.