Calcium Carbonate Precipitate, Cyanuric Acid Levels Falling Dramatically, Can't Maintain Chlorine Levels.

tux

Member
Feb 13, 2019
15
Australia
The title says it all really.

Thank you for taking the time to read this post.
Any assistance would be greatly appreciated.

Calcium carbonate (I have had this tested) is precipitating out of the pool water. Pretty sure this happens when the electrolysis cell is running.
Cyanuric acid levels drop very quickly.
Electrolysis cell can't keep up desired free chlorine level (4ppm)
The pool has been shocked quite a few times recently. On one occasion free chlorine was about 17ppm after adding sodium hypochlorite in the late afternoon and had reduced to about 3ppm the following morning.
Yesterday I swapped the electrolysis cell for another. I will know in a couple of days if this has had any effect. (I doubt it)

Recent pool test results and additions:
pool 2 forum share
Some links to pics in the sheet (last column)

Feed water:

Calcium Hardness: 12ppm

Treated pool with approx 0.5ppm ClO2 11/12/18

Ammonia level 17/2/19: less than 0.5ppm NH3

Pool And Plant:

In-ground, tile lined, concrete construction, approx 18000L

Plumbing circuit:
pool
pump
Prizma sampling take-off (Blue I Technologies)
Hayward cartridge filter
gas heater
electrolysis cell (SteriSel Pool Controls)
acid injection
pool

Solar heating circuit:
pool
pump (thermistor controlled)
collector
pool

Fountain circuit:
pool
pump
fountain
pool

Pump runs for 3 x 4hrs a day OR 24hrs a day (depending on usage) giving 7 times pool volume turn over per 24hrs (minimum)
Prizma tests 3 x day regardless

Testing equipment:

Palintest 25 pro+ Palintest (calibrated 11/2016)

Chemicals Used:

Solid (powdered) cyanuric acid (1000g/Kg) (added to skimmer box)
Sodium hypochlorite (130g/L available chlorine present as sodium hypochlorite)

Thanks,
Martin

edit 1:
Add recent analytic test results
Add some chemicals used
Add solar and fountain info
Add test equipment used

edit 2:
add recent NH3 level

edit 3:
added date pool treated with ClO2

edit 4:
added calcium hardness of feed water
 

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Last edited:

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
11,308
Bedford, TX
Martin,

I really doubt there is anything wrong with your cell... You simple have algae, whether you can see it or not..

Salt cells cannot produce FC faster than algae can eat it.

Knowing your FC does not mean anything unless you know the level of your CYA. The two must be kept in balance per this chart... Trouble Free Pool

I recommend you take a read through this... Trouble Free Pool

Thanks,

Jim R.
 

tux

Member
Feb 13, 2019
15
Australia
Hi Jim,

Thanks for your reply.
I don't think there is anything wrong the cell either, thought they do 'wear' out and I want to eliminate it a problem source.

I'll try some algaecide.

Any suggestions on why cyanuric acid levels are falling so quickly? And calcium carbonate precipitate?

Thanks for your time,
Martin
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
10,964
Houston, Texas
Hi Martin, welcome to TFP! Are you adding CYA after you see the levels drop? If so how are you adding it? Are you tracking the frequency and volume of your other chemical additions?

Don't bother with the algecide. It is a weak preventative at best. It won't clear an algae problem on its own and may add copper to the pool, which you do not want.

Your CYA levels should be around 70ppm using a saltwater chlorine generator (swg). The low CYA levels you average in your report will not protect the chlorine produced from burning off prematurely in the uv rays of the sun. When the chlorine burns off prematurely it can't oxidize the nascent algae bloom efficiently.
 
Last edited:

kimkats

Mod Squad
LifeTime Supporter
Jul 10, 2012
37,403
Tallahassee, FL
I am thinking there is *something* in the water that is causing you all kinds of problems. You have already done the OCLT (Overnight Chlorine Loss Test) and had a huge drop in FC. That alone tells me you need to do a SLAM as seen here: Trouble Free Pool

Let's talk about your water testing system. How is it calibrated? Can you make it test on demand? We have seen when the Pool Stores have the computer testing systems that are way off due to not being calibrated often enough. I want to make sure yours is working as it should.

I want you to do a "test" for me.
-Download our Pool Math: Trouble Free Pool or use the web bases one: PoolMath
-Test the FC
-Add enough liquid chlorine to get your FC up to 10
-run the pump on high for about 15 mins to mix things up good
-retest the FC
-come here and post the results

Kim:kim:
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
11,308
Bedford, TX
Martin,

I suspect that you calcium carbonate precipitate is caused because your CSI reading is not between 0 and neg .3... I know on my SWCG pool, if I allow my CSI to increase very much into the plus zone, I start seeing flakes of calcium in my robot pool cleaner. It is almost like a cream colored paste after the cleaner picks it up.. If you don't know already, our Pool Math app calculates your CSI for you.. Usually adjusting your pH and/or your TA will lower your CSI and fix the problem.

As a general rule, CYA does not quickly disappear unless you have a leak.. In some rare cases, if your pool was covered in the winter and ammonia is created, the ammonia will eat CYA like crazy.

Thanks,

Jim R.
 

tux

Member
Feb 13, 2019
15
Australia
Hi Martin, welcome to TFP! Are you adding CYA after you see the levels drop? If so how are you adding it? Are you tracking the frequency and volume of your other chemical additions?
Hi Zea3,
Thanks for your reply.
Yes I'm adding CYA. Solid (powdered) to the skimmer box.
All additions (amount and time) are recorded in the linked Google sheet (scroll far right)

Let's talk about your water testing system. How is it calibrated? Can you make it test on demand? We have seen when the Pool Stores have the computer testing systems that are way off due to not being calibrated often enough. I want to make sure yours is working as it should.
Hi Kim,
Thanks for your reply,
The Palintest 25 Pro+ (a table top unit) is calibrated by a dealer. Last and only calibration was late 2016 (no adjustment was required) Manufactured 2014
The Prizma is calibrated using the Palintest. I can do an on demand test.
I will do your test asap and get back to you.

Martin,

I suspect that you calcium carbonate precipitate is caused because your CSI reading is not between 0 and neg .3... I know on my SWCG pool, if I allow my CSI to increase very much into the plus zone, I start seeing flakes of calcium in my robot pool cleaner. It is almost like a cream colored paste after the cleaner picks it up.. If you don't know already, our Pool Math app calculates your CSI for you.. Usually adjusting your pH and/or your TA will lower your CSI and fix the problem.

As a general rule, CYA does not quickly disappear unless you have a leak.. In some rare cases, if your pool was covered in the winter and ammonia is created, the ammonia will eat CYA like crazy.

Thanks,

Jim R.
Hi Jim,
Thanks for your reply,
I measure water balance using the Palintest. It's a proprietary scale but is directly comparable to the Langelier Index. My results have always been with acceptable limits.
Yes, as I understand it, CYA is generally very stable. It is highly unlikely that the pool leaks, but I will keep it in mind.
The pool is only covered for short periods in winter. It is used all year round. I have checked ammonia levels before (just with a fish tank kit) Not even a trace. I will test again asap.

Martin
 

kimkats

Mod Squad
LifeTime Supporter
Jul 10, 2012
37,403
Tallahassee, FL
Martin, If you have an ammonia test kit then there is no need to do my test as that is what I was thinking about. IF there was any ammonia in your water the FC would drop FAST on the 15 min test. Most people do not have the ammonia test so we came up with the 15 min test.
 

tux

Member
Feb 13, 2019
15
Australia
Some initial post edits:

edit 1:
Add recent analytic test results
Add some chemicals used
Add solar and fountain info
Add test equipment used

edit 2:
add recent NH3 level

edit 3:
added date pool treated with ClO2

edit 4:
added calcium hardness of feed water

Martin
 

kimkats

Mod Squad
LifeTime Supporter
Jul 10, 2012
37,403
Tallahassee, FL
Things might get worse before they get better. The cloudy could be from the dead algae parts. Make sure to keep brushing to get every thing up and into the water for the filter to grab!
 

tux

Member
Feb 13, 2019
15
Australia
Hi all,
SLAM complete.
Things were good for a couple of days. Now basically back to square one; "Calcium Carbonate Precipitate, Cyanuric Acid Levels Falling Dramatically, Can't Maintain Chlorine Levels".
:(:(:(
 

splashpad

Bronze Supporter
Hey @tux, Sorry the troubles you are having! (just throwing some ideas out) It sounds like you might have CYA destroying bacteria? Or ammonia? (just a quick read through the thread)

Could you put your pool, equipment and test kit info in your signature please? (So forum members can reference it quickly) Thanks!
 

tux

Member
Feb 13, 2019
15
Australia
Hi splashpad,
Thanks for your reply.
Last ammonia level check (17/2/19): less than 0.5ppm NH3. I'll check again.
CYN destroying bacteria? Any info?
Will do.
Martin
 
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splashpad

Bronze Supporter
@tux, So just finished the thread, are you able to test all water parameters?
The FC is too low (just stating the obvious) :)

Are you backwashing the filter? (what type of filter do you have?) That could possibly contribute to the CYA not getting into the pool.

I would get an athletic sock put the CYA in it and hang it in front of a running return:
 
Last edited:

mknauss

Mod Squad
TFP Expert
May 3, 2014
13,634
Laughlin, NV
The best way to insure there is not an ammonia issue - if it is thought there might be - is to follow the ammonia protocol.

To check and defeat ammonia, if necessary, is to raise your FC in the water using enough liquid chlorine to get to 10 ppm using PoolMath. Circulate the pool for 15 minutes. Test FC. If at 5 or below, add LC to get to 10 using LC, circulate for 15 minutes, repeat until your FC is above 5 ppm after the 15 minute circulation.
 
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