We are yet to sort out the "Oak Use" question. Dave is scared to death of it and rightly so from his experience. On the other hand we use lots of oak and have never had a problem and in fact it helps a lot for obvious reasons. I guess it all depends. If you added a bunch of lime in building the pond I doubt the oak would cause a problem as the tannic acid would be offset. There are benefits in some cases to fish health from tannins.