I'm no expert but it looks like someone poured some chlorine down the side of your pool. I'm amazed however that it could do that though. Maybe it was granular and it sat on the side and bottom for a while and bleached it. I really hope the acid wash works for you, otherwise I would be talking to the PB or service company- whoever is at fault asking if you should contact your CSLB, the BBB or even an attorney if they don't want to help solve the problem together. The contractors should have a bond with the CSLB you might be able to access unless it has been too long. Find out how long you have before the bond liability expires too.