I am using a heavy duty Rubbermaid 100 gal tub to soak some large pieces of driftwood for an upcoming tank I am working on. I have been soaking in tap water (well water - no chlorine) for a few weeks, changing 100% of the water every 5-7 days. Now that most of the brown color is leached out, I have 2 questions: 1) should I be adding a small amount of bleach to sterilize any potential contaminants - if so, how much should I be adding to the 100 gal tub? 2) I have noticed a substantial oil slick on the surface on the surface of the tub every time that I re-fill it after a water change. I have no aeration or water movement in the tub and I assume something is coming from the wood to cause this. Do you think it is potentially harmful? Thanks.