| I use white kolorscape sand(playsand or general use) for my 120 and the bag states that it is mostly slica free. Now my tank has been setup for seven monthes with no bad effects. So with my experience I would say its ok to use silca based sand. The one thing to be careful about is the sand getting between the glass cleaner and the glass. Will scratch!!
The snails seem to enjoy it as will. I think if you're dosing your tank properly and testing on a normal basis, you shouldn't be soo worried that your substrate is buffering your water. And if that the only reason to spend hundreds of mmore $'s, than that in my opinion is not worth it.
Just my $.02!!
Mr. Tang
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"Hello my name is Mr. Tang and I'm a Reefoholic!"
120 gallon mixed reef Tank, 90 gallon Frag/grow out tank, and 100 gallon sump &
The birth of the 150 | 
