What recourse do I have for a pool renovation that is not what we expected / paid for?

We contracted a reputable pool builder outside Philadelphia to renovate our pool. The same company who we contracted with to renovate the pool also built the pool. Once the renovation was complete we noticed discoloration in the plaster. They told us it would cure over the winter, but it was worse when we opened the pool in the spring. The company sent out a plaster expert who concluded the water chemicals caused the discoloration and therefore it was our fault to resolve. We followed every instruction, waited as we were instructed, and now they are saying it was our fault. We are looking to understand what recourse we have for getting the services from the company to fix our pool