Small spots of algae causing heavy chlorine consumption?

berniedp

Silver Supporter
May 3, 2020
56
Saint Johns, FL
Pool Size
6400
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair iChlor 30
Hi all,

I've been seeing quite a bit of chlorine consumption over the past weeks (my pool was a tad milky last week but is crystal clear now) and finally went out to buy a K-2006 kit to do some better measurements (I used the Lamotte ColorQ2 before - I know, in hindsight, that was a stupid purchase) so I could follow the correct testing procedures.

FYI: my pool pump runs from 8am to 6pm.

Here's what the numbers looked like over the past few days (blanks = I didn't test that value that day):

MeasurementJuly 15 - 5pmJul 16 - 5.30 pmJul 18 - 5pmJul 18 - 8pmJul 19 - 6pmJul 20 - 6:30am
FC10.27 (lost 3.2 in 24h)3.6 (lost 3.4 in 48h)7.46.6 (lost .8)5 (lost 1.6)
CC00.20.40.20.20.4
pH7.67.27.67.5
TA1009080
CH450
CYA6575
Action taken:Added Acidset SWG to 25%added CL & CYA
set SWG to 35%

So it seems my loss overnight (based on the last measurement) is 1.6 and part of that is recovered during the day with the SWG set to 35 (which, according to the SWG calculator excel generates 2.2ppm in 10 hours runtime).

With the water being clear (the spots on the bottom are stains, not algae):
pool.jpg

I have a waterfall feature which is switched off but where I think the valve isn't closing 100% anymore so it trickles water onto the tiles - and that seems to be causing some algae (sorry for quality of picture but had to zoom in on my phone):
tiles.jpeg

Obviously something is causing my overnight loss and that needs fixing - I'm not convinced that just increasing my SWG is the solution.

Is it the algea on the tiles?

Anybody any suggestions on how to move forward with this?

Thanks,
Bernard
 
Last edited:
Thanks drsipe! SLAM it is...

Just wondering - when I pass the SLAM criteria (CC, OCLT, water clarity), I guess I need to leave my SWG disabled (or at lowest setting) to allow the chlorine to drift down, right?
 
The chlorine in excess of your CYA protection will burn off fast. To help it along What I did to not forget about it was just turn the SWG off for two days and then turn it on again when needed at the same setting as before. YMMV

If you can see algae you likely have a lot of unseen algae which is why it seems
To be keep coming back
 
Ps - the SWG by itself cannot overcome algae as it is a continuous trickle rather than all at once. Even at super chlorinate….
 
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I set it to 0 before I started yesterday morning. I'm still going - while my water is already crystal clear (it was milky at most to begin with), I am still loosing quite a bit of chlorine. I've been trying to think what could be causing it but will stick to it for a few more days, let's see.
 
I set it to 0 before I started yesterday morning. I'm still going - while my water is already crystal clear (it was milky at most to begin with), I am still loosing quite a bit of chlorine. I've been trying to think what could be causing it but will stick to it for a few more days, let's see.
It’s not likely to clear up completely in a couple days. Follow the SLAM process to completion and then chlorinate according to the chart and it should be fine for the future.
 
Scrub everything you can possibly think of including autofill, weir doors, drain covers, ladders, inside of ladders, light niches etc…
 

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Finally - SLAM completed 🥳 - lost 1 ppm overnight, CC is less than 0.5 since the water hardly changes color when I add the 5 drops (it's not pink at all, just not as clear as before the drops and reverts back with 1 drop of FAS-DPD reagent and the water is crystal clear!

Thanks all for your support through my 1st SLAM :)
 
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