Go for sand, I'm replacing the sand in my tank right now w/ a blend of black and normal colored sand, the tank will look two toned, with the middle gradienting into each other (I know eventually it'll all mix up, I don't mind I like the look, makes it look more like real mud/river bottom) I did decide to spring for the expensice Caribsea stuff, which supposedly reduces nitrates and such based on it doesn't let stuff seep into it as gravel or coarse sand.
If you don't go bare bottom (I personally don't like bare bottoms for habitation tanks, just for QT's and fry grow outs) for sure spring the extra loot and get the good sand. You'll kick yourself later for skimping on anything in your tank.
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