Algae back. SLAMed mid April, chemistry looks great. Why is it back?

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sonoman

Well-known member
Dec 27, 2010
51
Santa Rosa, CA
I SLAMed my pool in mid April after re-balancing pool chemistry after winter rains. Turned salt generator off, OCLT quickly stabilized, I let CL drift back to normal, and thought I was good. It's now mid-June and algae is back. Why is that? Not bad, but I see algae when I sweep the walls and steps and my CC is elevated to 0.5. My salt generator is working with Cl routinely in the 5-7 range, a little high. Why is the algae back and how do I keep it out?

Using TFTestkit
pH: 7.5
FC: 5.5
CC: 0.5
TC: 6
CH: 325
TA: 75
CYA: 70

With algae present, I will SLAM again. Normally, if I SLAM after the rains subside and maintain chemistry through the summer, it is good. Why did it return?

thanks
 
The answer is always low FC.

How often do you test ?
When do you test ?
What is the SWG runtime and %
 
Thanks. FC is my first reaction too. I test Cl every few days and it is stable, in the 5-7% range (a little higher than target for salt pool). I shouldn't have to maintain it higher than that...and I target the 4-5% range. I have the Circupool SG set around 30% duty cycle. I run the VS pump on low speed most of the day, high speed at night.

BTW, I did not include water temp, which is 74, and I changed DE filter media around Memorial Day, just after the oak tree pollen bloom.

I picked up some liquid Cl and will start the SLAM over again. Still scratching my head how the algae came back when Cl has been good/high since my last SLAM.
 
sonoman said:
Still scratching my head how the algae came back when Cl has been good/high since my last SLAM.
Click to expand...
You target 4 to 5ppm. SWGs, while more stable with FC levels still fluctuate throughout the day. You are dipping below min and algae is moving in. You need to set a higher target.

I overshoot target level and fall back into it, remaining free and clear above min at all times. I wish on all things holy that folks obsessed over having enough FC, as much as they do trying to squeeze by with too little. (Unsuccessfully, as you've seen)

swcg_chart.jpg
 
Whats your usual run schedule and % for the SWG ? We can math how much FC it should produce and compare that with the time of day to see why it's falling off.

For example, if you only run at night, it starts the morning at peak FC and drops until the sun goes down. If you test in the AM, everything looks great, but in the evening it may be low and you'd miss it. It would recharge overnight and look great again the next morning.
 
As I noted above, my pump runs most of the day at slow speed and at high speed for several hours each night. My old Hayward SWG was programmed into the controller to run at night and some during the day, and I don't remember the program loops because it has been a long time since I went into the program. If I remember correctly, the current Circupool generator, which I much better than the Hayward, runs independent of the controller program and runs on a duty cycle when water is flowing. Sometimes when I check, it is generating, while other times it is not generating and after talking the to Circupool support, that's because of the duty cycle "% generation" setting. I usually keep that setting at 30%, where it is today. Maybe I rolled it back too low, even though the Cl level reads correct when I check it (typically in the morning).

Your "it dips down enough at times of the day to allow algae growth" hypothesis sounds like something to watch
 
sonoman said:
As I noted above, my pump runs most of the day at slow speed and at high speed for several hours each night.
Click to expand...
We need exact pump run times to calculate what the cell should produce. 30% of most of the day, and 30% of several hours at night is a tad vague. :ROFLMAO:
 

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I set up the controller program 20 years ago for my my old Hayward SWG, so my memory is a little foggy. Also, the Circupool generator operates a little differently with the controller, with more local control on the Circupool unit. At the time I set up the program, it had multiple loops at different speeds and times to run the SWG and the solar mats. I calculated at the time what I thought was needed to turn the water over a couple times a day and I got good results, so I left it there. Electricity is super expensive here, 33c/kwh, so I wanted to run it longer at slow speed with less friction to ease the pain of my pool pump. Looking at my old pool notebook, I set up the program to run the pump at slow speed 8am-5pm and overnight at high speed 12am-6am.

I started the SLAM, taking FC up to 24 with bleach Wednesday night using PoolMath calculator. It initially showed a pale hint of CC, <0.5 CC. I added bleach during the day Thursday to keep FC elevated and after sunset Thursday tested at 23 FC with 0 CC and left it without adding more bleach. Tested at 6am this morning, Friday, and OCLT held even at 23 with zero CC. How long should I hold elevated FC shock level before letting it drift down and re-starting SWG? During my initial start-up in April, OCLT reached zero drop within a couple days so I let it drift down without holding the elevated level any longer.
 
27K pool, Day, pump 9 hours, 30% in your pool is 1.5FC.
You test in the morning and find FC = 4. If your daily demand is 3 FC, you will be below min at the end of the day. 4 + 1.5 - 3 = 2.5.
Below minimums and algae takes the stage.

If you target 7 for morning test...
7 + 1.5 - 3 = 5.5 Well above minimum...
 
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