Have been having trouble with green algae. Have an inground vinyl liner pool. Haven't had this trouble for 6 seasons. Had several pools techs out to the pool. Finally someone has told me they think I have too much CYA in pool and my shock had not been working. Discovered that my pool shock (sodium dichloro-triazinetrione) contains cya and also my pool tablets has cya also. Have you ever heard of this. I was told I needed to use Lithium hypochlorite shock. I have spent 600.00 now trying to get rid of this algae and it keeps coming back. Whats your take on this problem? Help