My tank is navigator a bit of a problem... everyone I do a water change I leave behind this whit residue in the water... which then turns my driftwood white and stays like this for a few days... tank is 4'x3'x3' housing my motoro rays and arowana ... my main question is...without buying R.O. water what should I do? My levels all test perfect but no matter what I do or use.. I continuously have this white almost chalky substance in my tank and water itself.... I can't even have any lights stronger then florescent or my tank has a white glow.... I run a Sump with a mag 12 and a fluval 405 with sponges and peat and carbon... guys and girls please help me...