I also confused on this since i got this issue before by using BIOS pellets.
IT was solved by dosing vodka and bacteria. Try to use. Different bacterial brands together. As i feel bacteria are picky for carbon sourse and tank. Haha. I tried 3 brands. Plus crazy feeding oyster fest.
Also my another tank was solved by algea scrubbers.which. is also very good for. U to try.i got one spare can lent u.
So. I suggest u to try Turn down The flow of ur gfo fr. And feed more and multiple brands bacterial dosing.
Algea scrubber works really well.