We have a concrete bottom, fiberglass sided, 25,000 gallon, 40+ year old pool with a ton of unsightly staining on the concrete that we have been living with since acquiring the pool in 2012. My guess is someone let it sit with debris and it ended in permanent staining. For aesthetic purposes only, we would like to drain it completely, then use a pressure washer and bleach to remove as much as the staining as possible. My sole concern is that I don't want the walls to cave in or crack and I don't want to float the concrete bottom (if even possible). What steps can I take to prevent any of these disasters from happening?
Thank you very much for the advice.