Pool Ladder Scaling?

I hope this is the correct place for this inquiry! I have a 3 year old used AG pool we just erected. It came with a white plastic ladder that lifts above and out of the way for safety. The water exposed ladder has white or light green "scaling" or dried stuff all over it (looks like dried milk, but much more persistant). I tried with a pretty stiff plastic brush to get this off. Does anyone know what it is and how to clean this ladder? Thanks for the info. Andy

Ended up using Works toilet bowl cleaner. Worked awesome and no scrubbing. Just another diluted form of Muriatic acid.

Thanks for the tip--sorry you didn't get replies sooner, but I guess you're the first one with that problem!

Janet