Thanks very much. I won't feel bad :) It's for the good of the fish. The flow is very low, just the moving leaves give the illusion on the video that it is on the high side. Although bettas are adapted to low oxygen levels, they live better and longer in oxygenated water and the water surface agitation is needed for that. And he swims exactly the same way when the filter is off during water changes, shaking his whole body so it's not the filter, I think his tail is a bit too heavy and I guess it's a bit of exersise for him :) He goes all over the tank so he doesn't seem bothered and he is quite lively, only goes in between the anubias leaves at night time so he can't be tired from the flow. If it was too strong for him, he wold hide and rest somewhere in a quiet corner. As for his fin, it was damaged already when I got him so that's not from this tank.