Tank cleanning

[khiemdong]

Hi
I just have a quick question. I try to clean my tank because it has some purple thing stick on the glass inside. That is too hard to remove them since it stick for so long. i try so many times but still can't remove that purple stain. I got a reef tank 45 gallons. Any help?

 

[nycbob]

sounds like coraline algae. many people use cutting blades to scrape it. i use my finger nails.