Yeah pool filter sand is fine. Many people on here use it. The one tip i can give you is to wash, wash, wash and when you think it's clean, wash it again!!!. Get a bucket and 1/3 fill with the sand. If you have access to a garden hose use this. Give the sand a good blast with the hose and give it a good stir. Repeat this over and over, until the water runs clear. The more you do this now, the cleaner the sand will be and not cloud your tank. It is a bit of a pain but the better you do this at this stage the better and clearer your water will look... When you refill your tank, put a dinner plate/saucer/bowl in the the tank, ans pour the water onto this and it will prevent turbulence and cloudy...
This process cleans the sand of dust and dirt. It also removes any light, floaty sand which will cause clouding... Happy Washing!!!!
PS... You WILL loose some of the sand, maybe 1/4 of the total, so get more than you need. I always have some spare sand in a bucket in my garage....