Hi, today we built a fountain out of some logs we picked up from a woodland nearby. The logs are basically chunks of a tree of some kind. We have them cascading down (about 4 high, 5-6 inches depth) and the water runs into the pond. However, after having water running for a while, there are bubbles starting to form in the pond. The bubbles are white (similar to washing up liquid in water), not air bubbles from the water breaking the surface. The pond became full of white bubbles and so far 4 fish have died. The fish are all acting strange, they're not swimming very fast and they seem to have some kind of layer on them. 2 koi and 2 rudds have died. The logs were washed down before putting in the pond with water. What can be causing this?