Algae Recurrence after SLAM


New member
Jul 7, 2020
Port Charlotte, FL
I've done the SLAM only to have green/yellow algae recur in 7-10 days.

15,700 gal pool, Florida, temps 94F+

Start of SLAM:
pH = 8.2 - adjusted to 7.2 (measured)
TA = 70
CYA < 30 (top of sight tube is 30 ppm -- so something less then 30)
FC = 0
FC after add = 15

Maintained FC 10-15 for a week

End of SLAM
Water crystal clear (like a FL spring)
No clouds when brushing
FC over night 10 ppm - 10 ppm -- no loss
CC next morning = 0

After SLAM
added CYA to 30 ppm (measured)
FC maintained 5 ppm
CC always zero
raised TA to 80 (baking soda)
pH 7.5 - 7.6

10 days after SLAM - green/yellow film & clouds when brushing
FC = 4
CC = 0 (how can that be?)
pH = 7.8
TA = 80
CYA = 30

Adjusted pH to 7.5
Raised FC to 11 (measured)

2 days after seeing algae again
FC = 11
overnight drop = zero (again, how can that be - there is still some algae)
CC = 0

I do not know what to think or do. With FC = 11, CC = 0, overnight drop = zero, I still see a small amount of algae when brushing. How can that be when with those measurements? And when does this stop? Why does this keep ocurring?

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Welcome to TFP! :wave: Are you sure it's algae? Something seasonal perhaps? Any way to capture some of it and maybe smear it on a white paper towel? Can you update your signature with all of your pool and equipment info, then perhaps post a pic of your pool so we can see what you have to work with? Include your test kit in the signature too. Maybe something will stand out.


Gold Supporter
Feb 19, 2019
Orlando, FL

I’m in Orlando and I’ve had the exact same experience. I kept FC in range and would inevitably see a green/yellow cloud when I brushed the pool floor. It never accumulated on the sides, only the bottom.

I would SLAM, pass all the criteria, and yet a week later I’m seeing green stuff on the pool floor. I once even maintained the SLAM for a full week after passing the criteria and then raised to mustard algae shock level for 24 hours. Still, the green stuff came back.

Meanwhile, I get a ton of pollen in the pool during the spring, which confuses the issue because it looks like algae.

What finally has seemed to work for me is to set my daily FC target to 3 ppm above the recommendation. So, I have 30 CYA, which according to the charts means a range of 2-6 ppm of FC. I add enough each day to reach 9 ppm. Since I’ve started that, I have not experienced the problem. I attribute it to my pool not getting enough circulation on the bottom, but that’s just a guess.

I hope that helps!
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