There is absolutely nothing wrong with silica based playsand. As long as it is labeled as "playsand" and not construction/traction sand it is safe in your tank and will cause no problems. The only thing lacking in regular playsand is PH
buffering. Silica causes no problems in a marine environment. If your tank is glass and not acrylic, the entire thing is composed of basically melted silica. If you want the PH
buffer then by all means change out your sandbed. If on the other hand you are doing it because you think regular sand is bad, then save your time. "Silicate" in the water is a bad thing, "silica" is completely different. Silica will not give you silicate.
For grain size, sugar is a good idea regardless of depth, but slightly larger will give copepods a better place to live.
, Ignorance IS bliss, and patience is a virtue. So you can have a pretty good life if you're stupid and don't mind waiting around.