So i have been using magic erasers, doddie pads and plastic scrapper to keep the tank clean. But I can’t get off this stubborn algae or whatever film it is. It’s hard to take a picture of, it’s only on the lower qtr of the tank. I almost feel like it’s etched into the acrylic or something. I scrubbed the same small areas for five minutes with all the above materials, it didn’t even touch it. Any ideas on what this is and tips to get right of it? The rest of the tank is crystal clear. This is so annoying! Thanks!