All sand is silica sand. The silica in sand is not soluble in water at all. If it were sand would dissolve over time. In fact very few silicate salts are soluble in water and they're relatively easy to precipitate out. It's possible that you're adding silicates with water changes if you're using tap water and it contains silicates, but you wouldn't know that without testing the water.
If your water has very high silicates you might be able to see that via precipitation. Depending on the salts you have available to test it you'd drop a few crystals in a glass of your water and dissolve them completely. If you get a cloudy mixture or small particles/flakes falling to the bottom something precipitated out of the solution. For silicates I'd try something like Epsom salts or calcium chloride (ice melt salt.) Either one could form a precipitate with other ions in the solution, but in drinking water you'd be most likely to get MgSO4 or CaSO4.