Lay Z Spa Hawaii 6 Person Hot Tub

Lay Z Spa Hawaii 6 Person Hot Tub in full working order but in need of a good clean.The hot tub is approx 2 yesrs old and was left with water in but without the filter running hence the staining to the inside. I have tried to clean it but being honest I could'nt find anything to remove the stains. It comes with the original repair patch and the under water adhesive patches. Unfortunately I cant find the manual but this available on line.