Hi hopefully someone can identify this for me. I’ve never seen anything like this before. I tried to manually remove it but it’s surprisingly VERY hard to scrape off even with a toothbrush. It’s a 6month old system 125 gal with a VERY LIGHT bio load(two clowns, a gramma, softies and hammers). Salinity 1.025-6 nitrates and phosphates 0. Low calcium(360ppm) and alkalinity(6) I’m working on bringing it up.