I cant figure out your problems but here's how i grow all my water loving phrags.
First on all, the temperature is mostly at 25 degrees Celsius during the day and it drops down to 18 at night
I water it ONLY with RO or distilled water, I find if I don't, they don't grow as quickly in the roots and that they get leaf tip dieback. This is not necessary but i think it helps a lot.
I also only fertilize once a month and I let the sit in a tray of water that I change every day.
also, the potting mix should not contain lots of sphagnum as, these plants still need air for the roots, and being wet all the time already limits the air. And being humid helps as well.
Thats all i have. Maybe your problem is the humidity?
because i know bessae tolerates heat better than some of the other phrags in its group. But then again 30 degrees is very hot for any phrag!