Could this possibly be HITH?

  • We are currently upgrading MFK. thanks! -neo
if them 'holes are symmetrical then its part bof the laterel line. . . if its random and not laterel, then its most certainly hole in the head.
 
From a closer look, the holes are kind of symmetrical - the other side also have some similar-looking marks. These are not really holes IMO, but rather deep streaks, but I could be wrong.

Anyhow, just to be sure, I'm doing wc twice a week for a couple of months to see if the situation improved or not. Also, I added another lightweight canister filter (Eheim 2215) to the tank to help with the filtering - I only had Rena XP3. And I threw out the carbon bags too.
 
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