Recently I've changed my mind on assessing aquarium state based on how quickly the glass fouls. I have three ~90% acro tanks with a high density of corals. Nutrients are always below levels of detection. In fact, some of my corals have poor color, which I think is due to low nutrients, so I even started dosing nitrate for a while, but wasn't able to get nitrate elevated at the max level I was willing to dose at. At the same time, i would get significant algae, mostly hair algae, growing on the walls of the tank after about a week. Even though the tanks have been running for at least a few years (one around 10 years), it was only ~6 months ago that I added a bunch of turbo snails to complement some tuxedo urchins (I'm not big on cleanup crews). Now, I never see much algae on the glass. Instead, the problem is now coralline algae, but I'm able to go longer (~1 mo.?) before that becomes excessive. So, the animal content of your tank makes a huge difference in what develops on the glass, so water chemistry is just one component. As usual for saltwater tanks, it's complicated!