I have been bring water samples to the pool store & adding the chemicals they prescribed. I replaced the sand in my filter but the pool is still green. This happened for 2 months last summer & now the same thing this summer. Please help.
The green water is a result of a lack of chlorine at some point that allows an algae bloom to start. Then it does not take long to take off and make your whole pool green. If this happened at the same time last year, consider the circumstances. High heat, increased bather load, etc. would require the need for additional chlorine. Or landscaping, fertilizing, debris in the pool, etc. also impacting the chlorine demand, but could also contribute the organic "start" for your algae bloom.