I agree on replacing it how ever dont throw it away . Rinse it out very well and then dry/bake it to kill off nasties , When you do a water change use that water to rewet it keep it in a dark container to avoid growth of unwanted algeas . I have done this with several of tanks....and never had an issue ... At $30 bucks (low end of the price) a bag I found that it works to rinse it very very well and dry it then rewet it to give you "new live" sand ... Baking it or drying it kills off anything that is not desirable (actually it kills everything) but it gives you a fresh set of sand to use in the future should you need to change out your tank. I have also used all my old sand when transferring tanks but also did a 50% water change and rand extra filters for a day or two to help remove anything bad , I rinsed the filters hourly the first day and daily after that then changed them weekly , then when it was all settled down and my tests continued to run 0 I went back to monthly changing and weekly rinsing