woke up to some algae green

sonoman

Well-known member
Dec 27, 2010
51
Santa Rosa, CA
We have been having hot weather (for us), 100F. Floating pool thermometer shows 79-80 at top 6"

Pool has been crystal clear since spring. Chemistry was easy to dial in after winter and has been pretty stable through weekly tests. Today's readings using TFTestkit (2024 reagents)
CL 10ppm (very high; see below)
CCL 0.5
CH 325
TA 110 pH 7.5-7.7
CYA 70-80
DE filter media replaced over Memorial Day weekend

This morning the pool has a pale green tint. Swept it down, very little dust/algae came off the pool walls.

An earlier post reply suggested the chlorine level dips down between duty cycle periods on the salt generator so I bumped up the duty cycle. Chlorine normally lives around 7 with CCL at zero. Today it read 10-11 with CCL 0.5.

I can initiate a SLAM to kill all the algae, which I assume is the prescription. But I am scratching my head to why it turned green with seemingly very high chlorine levels.

One last piece of the puzzle. I have not used my solar heater in over a year because some tubes leak and I need to replace a couple mats (and the salt water is rusting the shed structure it sits on so I need to repair it too). I ran it a few minutes yesterday to identify the leaking mats, then turned the diverter valve back to "bypass". I expected some algae in the plumbing to/from the solar mats, about 40ft away, but I did not see any debris or algae flushing out when I ran the heater (I did look). I expected to see a plume if there was something, but I also expected the high chlorine levels to take care of anything flushed out.

What do you folks suggest? SLAM? Then what?
 
I am not a pro at CYA test and it is difficult to read, as you know. I read 70-80 range today, which was a lot higher than I expected. My wife was reading 30-ish earlier in the year after the winter rains diluted the pool. We put some chlorine tabs on the pool steps (which contain CYA) and I put some CYA in the pool several weeks ago, but well below the PoolMath recommendation to avoid over-shoot. Looking for my wife's testing notebook now. She read 40-50 in May so I may be off. I can run again or wait for her to get back home
 
10 FC is not high for your CYA of 80(if in doubt we round up). In any case if you see green algae you need to perform a SLAM Process.
Doing so with 80 CYA is almos cost prohibitive. We recommend you drain at least half your pool volume to reach 40ppm and then slam.
 
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