I have a 18 x 36 inground pool, vinyl liner. I have clear water but have dark algae ( I think) on the bottom of pool and along some of the liner seams. I have had this issue for past 2 yrs. I am tired of going to the pool place because there has not been any improvements and what staff they have that will come to my home and provide chemical and testing , want $300 + dollars! I test the pool water and it keeps showing my chlorine is high....any suggestions for this frustrated pool newbie? Thank you for any help.