I boiled my driftwood numerous times until I wasn't getting much brown water. I added the driftwood to my tank and after a week or so the water starts turning brown. I'm running a Fluval 405 with carbon & a Tetra 30-60 with carbon. 50% water changes clear it up, but the upper corners of the tank stay dark like the glass is stained. Is the tannin staining the glass? If so, can I clean it without having to remove the fish?