I made a big discovery today, behind my pool light there was a very large deposit of black algae. Since last year I have been chasing a chlorine demand/ loss of CYA issue brought on by the premature failure of a new salt cell last year. The pool generally looks very good, clear water, no stains (as long as the SWG is working). This year I did a lot of research into disappearing CYA levels and came to the conclusion that it was caused by an algae type issue. I recently completed a 2 1/2 week SLAM process and the pool was in good shape.
During the SLAM I found some black algae around the pool light and brushed it clean. At this point I will tell you I thought the pool light was dry in behind bulb, now I know that is not the cause. I would not have found this problem if my Aqua Rite controller hadn't quit working early this week (burnt out current limiter, new one on the way from Digi-key). I started adding bleach this week and noticed I was consuming lots of chlorine again. I checked the light and gave it a tap and the black algae started coming out from the light. This prompted me to investigate further.
I have cleaned the light and the niche good. I vacuumed what I could as I took it apart and the robot is running presently. After the robot is done I will manually vacuum what the robot missed and then take the filter apart and clean the cartridge filters. I have brought the chlorine up to 16.5 ppm, reading the bit on black algae in Pool School this should be a good level to hold for the next few days. Below are my test results from this morning. The PH is high I will lower with muriatic acid after I clean the filters.
One thing I am finding is on my pool light there is a SS plate on the back of the light and there seems to be a build up of algae on areas I can't reach. I am soaking the light in a bucket of pool water with some extra bleach hopefully this will clear it up.
The funny thing is after I found the problem and start search through the forum I came across many post with the same problem. I am sitting here type and shaking my head because now it seems so obvious what was causing my issues. I thought I had a good handle of dealing with pool issues before I am discovering it is a evergreen process in managing the pool.
Please feel free to post any advice or comments. I have a bunch to get done as it is family pool party day as it is going to be 35c here today.