Hello, I have a mystery illness in a betta fish. He was perfectly healthy up until now, I noticed the other day he got a few ripped fins but those have healed. He is now swimming like he can’t keep the back of his body horizontally, he seems fine otherwise. He swims up and then conforms to like a forward bend c shape and sinks. I’m worried even more now because the fry he fathered are now presenting the same symptoms and they are in different tanks. I have since separated two fry out of the bunch. The water is pristine, and I have ammonia checkers. Any ideas?