For sand I would look into PFS (Pool Filter Sand). It is relatively cheap, although recently I found the price just went up...but for 50lbs you should have to pay much more than 10$. The nice thing with PFS is that the granules are large enough that they do not float they pretty much immediatly sink.
A good rinse out then I filled the tank 50% and used a large cup to pick up the sand put the cup into the water to the bottom and then turn the cup over, this didnt leave much if anyting floating in the water and within 10 minutes it was good to turn the filter on, although I still waited a few hours.
I did my 55g with 50 lbs of sand and it was plenty, so for yours just up convert and you should be good. I had pea gravel in mine and when I switch to sand the improvement was immediate with the fish. You will have a loss in bio material with the gravel though so it is best to do the change before your fish jump in the pool. Then get yourself some MTS (Malaysian Trumpet Snails) and you will good to go. I find my fish will even eat them in the sand...I am trying to get them growing in my 10g because everytime I introduce small ones into the large tank the fish eventually seem to sift them all out of the sand haha.
Good luck! Pics when you get it setup and fish in is a must!