What can I use to clean pool surface?

[DanaSC]

Last year we were told to drain our spa when we covered our pool and spa. We later realized that was a mistake, as all the water that got on the cover over the spa caused the cover to be pulled. We rigged up a way to keep that from happening by putting a wooden board across the spa. This year we won't drain our spa.

The wood we used caused a stain on the gunite within the spa. My husband wants to drain the spa down and scrub it before we refill it and winterize the whole thing. What would you recommend he use? Can he use Soft Scrub or something like that? Any advice would be much appreciated!

 

[Bama Rambler]

I'd first try some bleach to see if that lightens it. If it doesn't, try a Magic Eraser. If that doesn't work, try crushing some vitamin C tablets and rubbing on it. Being that it was wood it should be organic stains unless it was treated wood, then it could have some metals in it.