Need to make some clarification...
Inside glass isn't very dirty at all. I just zoomed in on the markings because they were very faint and were only visible at a certain angle under Verrrrry high light from the LED strips placed behind them for a better photo exposure. The zoom and narrow focus make it impossible to see the clean aquarium behind the glass. I'd never seen anything like this before becauseI keep the tank and water so clean... Obsessively so. I do water changes about tree times a week at 40%. I pre-treat and "age" water in barrels to the same temp and pH as the tank so the water changes are completely stress free. I keep up this regimen in preparation for the discus fish that will eventually be present in that tank. Very low nitrate ever. Also UV sterilization keeps algae at almost zero, and I certainly feed veggies and algae wafers to the BNs and SAEs.
~pH7, Aquarium Ninja
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