I find sand to be an excellent sub-strait. You just need to wash it really good before hand.
Put some in a 5g bucket and fill it with water. Get the water spinning really well such that all the sand is moving with the water column. Then let the bucket sit for just a few seconds and then quickly pour the water out along with everything that is still in the water column (without dumping the sand that has settled in just those few seconds).
Once you've done this a few times with each batch of sand (the batches have to be small enough that you can get all the sand up and spinning in the water column at first), you will be left with a some very dense sand that will easily sink to the bottom of your tank and never get hung in the water column.
Once rinsed well, you should be able to fill a tank with water, dump a bunch of sand in, and in less than 1 minute, the water should be clear.
What I will say about pool sand specifically is that it is a very large granule sand... actually something on the order of tiny rocks. I find play sand or other fine sands to be much more appealing in a fish tank.