Pool filter sand is nice but it isn't as fine as the sand you can buy from home depot or lowes, your smaller fish will have a hard time mouthing the substrate. I had the pool filter stuff for about a year in 30+ tanks, the fish like it but I noticed that the substrate would eventually become stiff and eventually need to be rotated when I did water changes. Its also like $15-$20 a 50lb bag compared to $3-4$ for the home depot play sand. I would pour the sand into a bucket about half full and rinse at least 10x before adding it, if you skip out your tank will be cloudy for some time. Its ok to keep your fish in the tank, use a cup and scoop it out of the bucket. Your tank will be much cleaner once the sand is settled, no more food or poop falling between the rock, everything makes it to the filter if you have good water movement.