My Seaclone 100 does this every once in a while. What you need to do is take it apart and soak it in 4 gallons of water and a capful of bleach. this will really clean it. Make sure to rinse it well and let it dry preferably in the sun and before placing back on take rinse it out again with cold water. Also you want to make sure the sponge filter on the inside of the tank stays clean. If its not very clean well its not gonna be as effective. Just my 2 cents.