Okay so I have a 10 gallon tank and o have a aqua tech 30-60 gallon filter and sand my tank keeps getting this white build up on thw glass and when I scrape it of it comes of but comes back in a few days I so water changes about once a week. And the tank only has one fish ( red tail catfish) and he's a baby. Any suggestions? My water does have extremely high iron could that be it?