I filled a 5 gallon bucket 1/3 full with sand, then ran the hose into, constantly stirring it up. The lighter stuff you don't want floats out as the bucket overflows, and the heavier sand stays behind. Keep this up till the water clears itself in one minute after pulling out the hose.
oh arogonite, yeah use a strainer. thought you were using finer sand. check other post for adding it to established system, still do it that way for arogonite.
a mixture of different sizes is always good, but it is mostly what kind of look you like. Some people like just the fine sand look, and others like the mix. Both are fine!