In switching beds, I always recommend changing about 1/3 per month. This gives the new third a chance to grow the proper quantities of bacteria.
As for which sand to use, or should you, there is more info than you could read in a year on the subject. Sugar sand is popular for deep sand beds, which have become less popular lately. It also blows around if you have excessive flow. The aragamax select is a bit heavier, and acts the same in deeper sand beds. Some people have gone bare bottom, or other methods of covering the bottom glass.
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Brad
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