what type of sand to use?

do a search under "sand" and this will bring up some info as well as other suggestions.

I am pretty sure you should use play sand.

I have used playground sand purchased in bags at Lowes. Be sure to let it thoroughly dry before filling. An alternative which I recently tried on a pair of speaker stands is kitty litter. The kitty litter was easier to use simply because it did not require drying. Please don't ask me which sounds better, I don't have golden ears.

Get what's labeled "White Play Sand". It's very fine and easy to work with.