Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
From a salt water beach a thorough rinsing will get rid of the salt. Diseases or parasites from salt water usually cannot make the transition to fresh water, so I would not worry about that.
From a fresh water beach a thorough rinsing will get rid of organic matter like decomposing leaves. I would also boil it. Stuff from a fresh water source can also bring in disease or parasites to a fresh water tank. Put sand and water on the stove (or do it outside, on a BBQ) and bring it to a boil. Just a short time is OK.
Then I would test the sand to be sure it is not from coral or limestone. Put some fresh water in the bucket with the sand and test GH, KH and pH. Test again in a few days or a week. If there is no change then this sand is good for a soft water tank. If there is a change (GH, KH or pH rises) then this sand is OK for hard water fish like livebearers or Rift Lake Cichlids or certain Rainbows.
Look at what settles, too. If there is a scum of fine stuff I would try to get rid of it, not put that fine stuff in the tank. It can make the water cloudy or it might contribute to the sand packing down and becoming anaerobic.