Mark, Tanin blackens the water. I totally destroyed my pond when it was first built. I had the dozers put a huge pile of recently cleared green post oak in for fish habitat. Rain came and within a week, the water blackened. After many chemical tries, I finally pumped it dry and let the Texas summer dry the wood and mud. The stuff was lethal to stocked fish and other life. Cows and wildlife stayed away but we had to move the much dumber horses. Bob Lusk once posted on this regarding tanin effects relating to soil types and resulting water consequences. I'll never take that chance again!