Using Caustic Soda to neutralize Cyanuric Acid

[SorensenR]

We are about to return to the house and I will start to install and test the bleach dosing pump, but since I am still short on rain water let me share a picture of my 10,000 gal holding tank.

 

[mgtfp]

Impressive. Are you hunting for Neutrinos?

 

[SorensenR]

Impressive. Are you hunting for Neutrinos?

Yep, but they are slipping through my filters.
I am capturing rain from the back, front and part of the balcony roof.
We get about 80" of rain here annually, with about half of that during a very intense monsoon season.

 

[kimkats]

What a wonderful thread to read! So many great helpers to guide you in the care of this wonderful pool! Well done all!

LOVE the pic of the happy child! What a great smile and I can just hear her laughing!

 

[SorensenR]

I am back on the island and have activated the K-2006 test kit.
First off, I had to add 1,200 g (42 ounce) of caustic soda to get the pH back up to 7.2.
My cyanuric acid level is approaching scary numbers around 250-300 ppm, but I am desperate short on water in the neutrino detector, so I can't fix it for now.
I did a FAS-DPD chlorine test and got the following results:
FC = 9 ppm
CC = 1.5 ppm
Both results seem unusual high and there is no chlorine smell what so ever.
Could the high cyanuric acid level distort the test results?
Other than that, the water looks clear and feels nice.

 

[mgtfp]

Bummer about low water in the neutrino detector, you could really do with pretty much a complete drain and refill.

Your FC is actually not high in relation to your CYA level. Following the FC/CYA Levels, your FC should be about 12.5% of your CYA-level. For a CYA of 250ppm (did you do the diluted test? You can't really extrapolate the scale on the CYA test tube.) that would be about 30ppm FC - most of the chlorine is bound to CYA where it is not available for disinfection, oxidation and algae control. In terms of "active" chlorine, 30ppm with CYA 250ppm would be equivalent to 0.12 ppm with no CYA, or about FC 6ppm with CYA 50ppm.

The CC is so high because you have basically no active chlorine available to finish off the oxidation of combined chlorine.

I guess it's only a question of time until the pool turns green. You follow the SLAM Process, but with CYA that high, you'll need to lower that first. But you seem to be on restricted water resources, which is a problem.

 

[Mdragger88]

What is your ta? That effects how much of each chem you need to use to lower or raise ph.
Do you have a ph meter?
They can be helpful for checking ph with fc levels above 10ppm (which you need to be maintaining) They do need to be calibrated regularly & checked against the ph test in your kit on a regular basis. You may need to use your tap water or a diluted pool sample to check against as the ph drop test is skewed at fc levels above 10ppm.
Bottom line
.... "Min FC" is 7.5% of the CYA level (that’s 22.5ppm if you’re cya is 300)
.... "Target FC" is 11.5% of the CYA level
.... "Yel/Mstrd Min" is 15% of the CYA level
.... "Shock FC" is 40% of the CYA level
.... "Yel/MstrdShock" is 60% of the CYA level
Get your fc up ASAP with liquid chlorine!
You can’t see pathogens so clear water doesn’t always equal safe water.
If you have discontinued use of the acidic tablets & have a ta of at least 50/60 your ph should not continue to decrease.
Aside from exchanging water the only way to lower cya is reverse osmosis- not sure if that would be an option for you.

 

[Mdragger88]

Also - were you unable to aquire borax or washing soda?

 

[SorensenR]

The penny finally dropped for me as how to understand the CYA/chlorine equilibrium. Thanks guys.
I did a 1:4 diluted test, which came out at 75 ppm cyanuric acid, so I am stuck with 300 ppm.
Adding 3 litre of 6% bleach will give me +15 ppm FC or a total of 29 ppm FC. I will try to maintain FC at that level until we get some rain in May.
TA is 60 ppm, so a bit on the low side. Adding 1 kg (35 oz) of baking soda or sodium bicarbonate will add 50 ppm. Good idea?
I don't really want to add borax as it seem to deviate from my strategy of installing the bleach dosing pump and eventually switch to the in-pool salt water chlorine generator.
I don't have a pH meter, but I have several titration kits in the range from 4.5-9 pH.

 

[PoolStored]

TA is 60 ppm, so a bit on the low side. Adding 1 kg (35 oz) of baking soda or sodium bicarbonate will add 50 ppm. Good idea?

Your TA is just fine. Don't add anything to adjust TA. Just manage your pH for now. Only adjust TA if it is below 50.

 

[Mdragger88]

We’ll do a rain dance for you!
Borax (borates) won’t affect your ability to have a swg in any way.
You just don’t really need it at this time since you already adjusted ph & we don’t add things we don’t need
Print this out & put it in your kit

Along with this

 

[mgtfp]

I don't have a pH meter, but I have several titration kits in the range from 4.5-9 pH.

The reason Mdragger88 asked about the pH-meter is that many of the drop based pH indicators get affected by higher FC levels (that you'll have to maintain until you get your CYA down).

The R-0004 phenol red for example starts to turn into chlorphenol red above FC 10ppm, which does the transition from yellow to red already at lower pH, so that it basically always looks red at typical pool pH, which leads to false high pH readings.

There is a workaround when no pH-meter (which doesn't get affected by high FC at all) is available that works up to about FC 20 ppm: You can dilute your water sample 1:1 with distilled or deionized water (this is important, tap water doesn't work as it usually contains chlorine and Alkalinity). As distilled water contains no chlorine, the dilution halves the FC. And because it also hardly contains any Alkalinity, but the pool water sample does, a potential pH change from adding the distilled water gets buffered away by the pool water. With this method you can at least test pH whenever FC drops below about 20ppm.

 

[SorensenR]

I have monitored FC for the past 7 days and it is dropping 3 ppm/day. This is equivalent to 600 ml of 6% bleach, so I have installed a dosing pump to add 300 ml twice a day, 6 am/pm.
I have a 12 gal reservoir, so that should last for just over 2 months usage.
I guess the next thing to watch out for is a slowly raising pH since bleach has a relative high pH, right?
The last picture is the underbelly of my little pool.

 

[mgtfp]

Well done with the dosing pump.

The chlorination cycle with bleach is pH neutral. Adding bleach raises pH, once FC is back down where you started, pH is also back where you started.

But pH will have raised in the meantime due to CO2 outgassing. The higher the TA, the more CO2 outgassing, the faster the pH rise.

While you were chlorinating with trichlor, this pH rise was hidden by the acidity of the trichlor. Now you will have to reduce pH from time to time with muriatic acid.

 

[kimkats]

Well done on finding something that works for you! I have been wanting to see how that was built and held up. Thanks!

 

[Heard]

I don't have a pH meter, but I have several titration kits in the range from 4.5-9 pH.

Electronic pH meter pens are readily available for purchase on Lazada.

I've initially ordered an expensive Apera branded model from abroad - it has arrived with a broken pH probe.
Then locally purchased a similarly looking but much cheaper Chinese off-brand model which works fine.
It's super convenient to use and fairly accurate.

 

[Heard]

The last picture is the underbelly of my little pool.

The view is terrific.

Sorry, I couldn't help but notice...



Do horizontal beams show exposed rusting rebar?
Make sure to inspect the structure if haven't done already.
Any exposed metal will quickly rust in that environment due to sea salt aerosols.
Rust on the surface of the rebar could cause further corrosion of the reinforcements.
Also make sure that there are no leaks from the pool and chlorinated water doesn't get into concrete.

 

[SorensenR]

What a wonderful thread to read! So many great helpers to guide you in the care of this wonderful pool! Well done all!

LOVE the pic of the happy child! What a great smile and I can just hear her laughing!

Thanks for your kind comments. The youthful laughter is bound to continue for many years to come as we had a small "accident" during one of the national Covid lockdowns where we stayed 8 months in the cabin. There is after all a limit to how much Netflix a guy can watch.

 

[kimkats]

and what a cute "accident" she is!