Maybe a bacterial bloom? Or it just could be a cycle of macroalgae. I have some similar on some of my newer tonga branch rock that wasn't fully cured. It popped up quickly but it's going away now.
Mine was recently in rocks that were two years old. After the treatment it all went away. How's your di canister? Mine was registering higher than normal Tds. I changed that out about the same time I dosed chemi clean
Just installed a new one I'm usually at 0 but I'm currently at 1. I think I'm due to replace my filter cartridges. I just replaced my membrane and switched from dual smaller di canisters to a single larger
