You need to know if that sand has parasites or bacteria living in it. You also need to know if that sand will alter the pH and/or hardness of the aquarium water. Do you know what the sand is composed of?
For bugs, bleach is the thing to use. Use a light dilution of bleach to water--you'll just be able to smell the bleach. Then rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse, rinse,
rinse, rinse, rinse, rinse, rinse....
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