I used "quik-rete" playsand in my 55 for over 2 years with no problems, algae or otherwise. Any grade of sand labeled "playsand" has to be essentially sterile. If your kids can eat a pound of it and be ok, it is fine for your tank.
I have a different brand in my new tank because it was lighter colored and smaller grains, also with no problems. It has quartz flakes and other little things that make it look nice. My
PH at tap is 7.9 and I buffer replacement water change water to 8.2 after the salt is mixed, It stays at 8.2 with no additional buffering. True, basic sand will not help buffer your
PH. Some people will advise you to stay away from other types of sand because they contain silica, which they erroneously believe will cause algae problems. This is because many people confuse silica with silicate. Silicate may help fuel algae, but even with 0 silcate in your tank, you will still have algae to some extent. It is pretty much unavoidable as long as you have water, food, and lighting.
FWIW:
silica : A white or colorless crystalline compound,
SiO2, occurring abundantly as quartz, sand, flint, agate, and many other minerals and used to manufacture a wide variety of materials, especially glass and concrete.
silicate: a salt or ester derived from a silicic acid; especially : any of numerous insoluble often complex metal salts that contain silicon and oxygen in the anion and constitute the largest class of minerals
Glass is basically melted silica, and therefore you will always have massive amounts of silica in your tank regardless of your sand choice. The ocean bottom is not covered with aragonite, it's covered with sand. Any playsand will be fine.
