I have a Waterbox 50.3 AIO I picked up second-hand. After getting it a bit more cleaned up, I noticed both side panels have a bit of hazing to them, and I can see quite clearly where the powerheads were as distinctly transparent (in the case of one on each side that was obviously never moved) or more or less transparent, in the case of a couple of smaller circular spots, indicating powerheads that were added/adjusted later.
So far, I have tried using a brand new sponge with a plastic scrubby side using first white vinegar, and later, citric acid, to clean it up, but don't seem to have made even the slightest dent in it.
Does anyone maybe happen to have any experience with this? Interestingly, it's only on the sides of the tank, not apparent on the front glass at all.

So far, I have tried using a brand new sponge with a plastic scrubby side using first white vinegar, and later, citric acid, to clean it up, but don't seem to have made even the slightest dent in it.
Does anyone maybe happen to have any experience with this? Interestingly, it's only on the sides of the tank, not apparent on the front glass at all.
