I'm having trouble keeping my bottom clean (not slippery). I don't know if the water is balanced correctly, but it is crystal clear, except every 2 or 3 days i see brown spots on the bottom and I will clean the bottom and the walls, but cannot figure out what is making the bottom slippery. Here are the current test results: fc 7.0, cc 7.0, ph 7.8, ch 175, ta 120, cya 50. If anyone has any idea,I would be grateful and Thank You in advance.