I'll get it done ASAP. Unfortunately it's not just money, but also time. I'm sure it would be kind of a venture. Might be able to get it done this weekend though. Canceled some stuff, and I can skip video games just this onceNothing is an inexpensive as a bag of Quikrete Play Sand. About $5 or $6 in US ($6-7 here in Canada), from Home Depot or Lowe's. The Quikrete Play Sand is safe on all counts. Not all "play sand" is. One 25kg (50 lb) bag will more than suffice a 3-foot long tank. I used one bag in my 4-foot 70g even.
It does make a difference. I used fine gravel for 15 or more years until those who know convinced me to change. I did notice a difference in the cories, though I would be hard pressed to say exactly what it was.