The Chlorine Mystery - two brand new chlorinators, balanced water, no chlorine

Jump to latest Follow Reply
N

No Chlorine for Old Men

New member
Apr 30, 2025
2
Perth, Australia
Long time lurker, first time poster, be gentle :)

The chlorine in my pool keeps dropping down to 0 after installing two different brand new chlorinators. Tried everything, including pre-emptive phosphate starver treatement. Help... :(

Historically used vintage metal box Kchlor AC20 non-self cleaning chlorinator kept the chlorine well, then failed.

Two months ago I replaced it with Freeflo RP25 self cleaning chlorinator. Water chemistry tests were balanced and salt level ok as confirmed by tests in three different pool shops. The chlorinator produced a lot of bubles, but the chlorine kept dropping down to zero after I top it up with liquid chlorine. Returned chlorinator after 1 month.

A month ago pool shop installed AstralPool E25 self cleaning chlorinator. Water chemistry tests were balanced and salt level ok as confirmed by tests in three different pool shops. The chlorinator produces a lot of bubles, but the chlorine keeps dropping down to zero after I top it up with liquid chlorine.

Total Cl: 0.16
Free Cl: 0.09
Combined Cl: 0.07
Salt: 4878
Ph: 7.5
Alk (adj): 110
Cya: 61
Hardness: 345
Phosphates: 0
Total Cu: 0

35,000 litre, concrete pool, in-ground, plaster, blanket
Sand filter, more than 10 years old
Peristaltic HCL doser
Solar heating was on, now off with the same result
Non-variable pumps, more than 10 years old
AstralPool E25 self cleaning
Chlorinator at maximum setting
Robot pool cleanter
Running 8 hours a day (8 am to 12 pm, 1 pm to 5 pm)
Water clear, but goes murky if I stop manually adding liquid Cl every day

Not sure if it is relevant, but the first two chlorinators used to produce white powder (CaCO3?) ouf the jets, the third one does not.

https://www.poolbarn.com.au/wp-cont...905-H0712400_REVB-AstralPool-Eseries-2023.pdf

I am aware that testing water yourself using Taylor test kit is more precise and I am planning to buy it in the future, but at this time I am relying on pool shop tests. I have tested water in three different pool shops who are using different test equipment with results showing similar results of balanced water and acceptable salt levels.

Your help will be greatly appreciated.
 
Last edited:
No Chlorine for Old Men said:
AstralPool E25 self cleaning
Chlorinator at maximum setting
Running 8 hours a day (8 am to 12 pm, 1 pm to 5 pm)
Water clear, but goes murky if I stop manually adding liquid Cl every day
Click to expand...

Welcome to TFP!

Your saltwater chlorine generator (SWG), running 8 hours per day, will add 5.7ppm free chlorine to your pool. With enough CYA, that should be enough to maintain the pool -- to keep it algae-free and sanitized, even in strong sunlight -- but it isn't enough to kill existing algae, which you clearly have because your pool gets murky as soon as you stop adding liquid chlorine.

You need to follow the SLAM process to rid your pool of algae. An Overnight Chlorine Loss Test (OCLT) will tell you when you've succeeded. At that point -- not before -- you can add CYA to bring the level up to 60 or 70ppm, and from then on the SWG will keep the pool clear.

The only problem is, the SLAM process requires you to have your own accurate CYA test and your own FAS-DPD free-chlorine test. The kits we usually recommend (from Taylor or TFTestkits) are not very readily available outside the USA, but we have some members from Australia -- perhaps one of them will reply with information about kits that are available to you.

In the meantime, some reading:

SLAM Process
Overnight Chlorine Loss Test
Test Kits Compared
Pool Care Basics
FC/CYA Levels
 
Good day Drew. Thank you for your prompt reply.

Wow... Okay I had a closer look at a far flat surface of the pool floor and I can see the faint green algae layer. Your explanation makes an awful lot of sense. I mentioned something similar to two pool shops and none of them believed that this is the cause and recommended to phosphate starve the pool and return the first new chlorinator because it was faulty...

Is it worth increasing the Chlorine levels while I am working on getting the FAS DPD Taylor test?
 
No Chlorine for Old Men said:
Is it worth increasing the Chlorine levels while I am working on getting the FAS DPD Taylor test?
Click to expand...
Yes, add 5ppm per day of liquid chlorine, nothing else.

Download Pool Math, use the same username/pw at TFP, configure your pool, share logs with TFP...then we can see your test results. Link-->PoolMath
Use "Effects of adding" feature to determine how much liquid chlorine to add to get 5ppm.

The test kit you need in AU is here:

When you get your test, post results and start the SLAM process. Link-->SLAM Process
 
Last edited:
No Chlorine for Old Men said:
Is it worth increasing the Chlorine levels while I am working on getting the FAS DPD Taylor test?
Click to expand...
The usual advice here, for people in your situation, is to add 5ppm per day of free chlorine while you wait for your test kit to arrive. That will help to keep the algae from getting any worse.

For your 35000 liter pool, 5ppm is 1.4 liters of 12.5% liquid chlorine (or 1.75 liters of 10%).
 
  • Like
Reactions: PoolStored
You must log in or register to reply here.
Top Bottom
Back
Jump to latest Follow Reply