Those don’t look like pond water bubbles to me. The surface tension is wrong. I see a film I believe as well. Something is getting in there. I must have missed the info on your water supply. Also I normally don’t recommend products to often but SEACHEM PRIME and SEACHEM STABLE. Read up on them. Nice pond! I have a 355 gallon with a 950gph pump and homemade gravity filter. My 7 comets went in the day the water did. My NH has never been close to .25ppm. Currently zeros across the board. Water lettuce, hyacinth, hardy lilies and native rushs.