Hi Krish's bettas,
Well you don't like wasting words do you mate.
Start by checking your co2 levels properly with a drop checker, its a complete waste of time quoting BPS figures as firstly they aren't of uniform size from one setup to another secondly it very much depends how big the tank is and how much is gassed off by the flow.
Poor co2 is usually the culprit. Once your absolutly certain that you have 30ppm evenly distributed throughout the tank you can look into other things but its really not likely to be anything other than a poor co2-lighting issue.
Ammonia levels would be the second thing I'd look at.
Regards, Chris.