jiml2083

those dont look like critter marks to me they are to square. Is this a acrylic tank?

Nope. Glass.

do u clean the glas on the inside with an algae cleaner? the ones on the magnets forgot what they r called having a big blonde moment sry...lol

@diablo30xp what's wrong with those algae cleaner on the magnets anyway :-)?

It looks like something on the outside of the glass, like a cleaner or something that dripped there? (sorry to ask the obvious) but have you cleaned the outside of the tank with a towel and glass plus sprayed on the towel?

I can't tell what it is either. Clean the outside with vinegar and water. Then try cleaning the inside with something made of plastic, like a credit card. Take your time and focus on one area and let us know what you discover.

Credit card didn't work and I am pretty religious about cleaning the outside of the tank. Any drip or finger print gets wiped up with R/O water and the stubborn stuff gets some vinegar. Could I use some vinegar on a rag wipe the inside and see what that does? The vinegar residue on the glass won't have a negative effect on the tank, correct?

With livestock in it? It'll lower the pH of the tank. You can drain the water if all you have is liverock, but I think you'll find this is going to be more than simply swiping the glass with some vinegar. However, give it a try and let us know. Maybe it is a thin coating of Kalk dust?

you could drop the water down on your next water change and put some jewelers rouge on a damp cloth and rub it with that and see if you can get any of the high marks off. That might give you a little better idea what your up against. I still stumped after looking at the photos several time, has it always been there or is this a new thing?

Did you try a razor blade? I've seen some pretty tough thin algaes before.