My ground water 1/2 acre pond was finished in January of this year. It found a level that was around 3 feet below the banks. I stocked FHM and CNBG in February. After several spawns I stocked 20 native LMB in july. The water has been a nice green and stable. Then came the rain. My land is scrub oak with approximately 200 trees on five acres. I keep it clear but I have years of leaves mulched. I got a 20 inch rain event at the end of July that overflowed the pond(I was surprised because its all sugar sand) The water turned black from oak tannin but returned to green after a week. The water dropped about a foot and stayed there. Then came September. Since the first of September I've received over 40" of rain. My 1/2 acre pond is now 1 acre of very black water with YOY living in 6 inches of water that covers the overflow. I am getting a little FA on the banks but my water is staying very deep black for almost two months. (I Know the answer is "It depends")But do I need to be concerned? Is there anything I should be doing? I feed twice a day, I have not had a fish kill, The 10" male CNB are a deep black color

I don't think the tannin will kill your fish unless the PH gets too low. It will reduce growth especially if you don't feed. I think I would have the water tested just to see if you need to make adjustments to PH and hardness.

Do you have any secchi disk readings?

I have not tested my water at all. I'm in the first year honeymoon, and with everything I've read on this site I thought all this pond stuff was too easy. I'll get readings this weekend and test my water (I have friends in high places at the water department)