There is nothing wrong with using Galveston sand as long as you take into account that it is a Silica sand, not Calcium Carbonate. It won't buffer the tank as well as a Calcium based sand, but a lot of people don't use sand at all and have no problems with pH and alk. The grain size is smaller, so it packs itself down more, which can be good or bad depending what you are going for. A smaller grain size means more of it will go into suspension in the water column. This can be a problem for magnetic impellers in pumps and powerheads, so try not to stir it up too much. Some seagrasses do better in silica sand and many digging inverts like it a lot better than coarser Calcium sand. It will provide a constant source of bio available Silica to the tank. This is great if you have sponges, but can be a problem since Silica is a limiting element in diatom growth, and too much Silica can help diatoms take over a tank in the early stages. As long as you supplement on a regular basis and keep the water quality stable, you should not have too many problems using Galveston sand. At least you can replace it if you don't like it and not worry about having wasted money since it was free.