04-22-2013, 09:12 AM
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Yah the sand goes to the bottom. If you really wanted to cover the blue you could, but you would need enough sand to fill the gravel space then enough to sit on top of that. The gravel doesn't really float to the surface of the sand, it just look s that way when the sand filters down through it over time... unless you constantly stirred it up.
I wouldn't recommend leaving the blue in the tank though... even if all you did was to scoop out most of it, it would be better. Dissolved organics are in the water, all you would be losing would be some rotting stuff that you really don't need in there anyway.