I purchased the par meter 3 months after ATI powermodule installed. I started hanging the fixture at 10 inches above water level. The par reading at center of water level is 950 (3 months old T5 bulbs). Three months later (6 months old T5 bulbs), the par reading at the same center of water level dropped to 720 drammatically. So I decided to lower the fixture to 5 inches above the water level. The par reading was back to 950. Ever since, the par at the center of water level always stays around 950.
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