Pool & spa still eating chlorine like there's no tomorrow

[Eddles]

Hi guys,

So, in April, I took over looking after this indoor 66,000 litre swimming pool and 12,000 litre hot tub from my father due to dementia. I've been having massive problems with chlorine and to a lesser extent TA ever since.

At the moment, the pool and hot tub both eats chlorine like there's no tomorrow. Ever since April, I've never managed to get chlorine of the pool over 1 and the hot tub over 0.5 even after pouring buckets of chlorine in them - at one point I was putting 1250g chlorine granules in the pool and 200g in the hot tub daily but the DPD-1 test showed barely above zero. I know I'm not over-chlorinating it as I've done the diluted test to double check I've not over chlorinating the pool. Also, when doing the chlorine test and after using a DPD-1 tablet, and it shows a result of zero, but I put the test tube to one side for 15 minutes, and after this time, it gets ever so very slightly pink if I hold it up to a very bright light. When I pour the tube down a white ceramic basin, there's a slight pink tint to the water.

Recently, I decided to change to 20g & 200g chlorine tablets, specifically those, to see what happens. The packing said that one 200g tablet in the pool skimmer will last 5-7 days, and one 20g tablet in the spa will last 2-3 days. Okay, so one 200g tablet in the pool skimmer, and one 20g tablet in the hot tub skimmer. Next day, the 200g tablet has shrunk by 50% and the 20g tablet was completely gone. DPD-1 testing both showed a chlorine result of zero. I put in another 200g in the pool skimmer and 2 x 20g in the hot tub, next day the original 200g tablet was gone and the second 200g tablet was 75% gone. The two in the hot tub was both gone. DPD-1 testing... a big fat zero for both. pH is quite stable for both, currently 7.2 for the pool and 7.4 for the hot tub. Hot tub water has been changed a week ago, so that's fine. Pool's TA is very high, CyA negligible. The pool has a UV filter which helps the pool to stay clean.

I've swam in the pool a few times and purposely opened my eyes underwater a few times and no red chlorine itching, but the water tasted kinda funny. Where is all the chlorine going?! It's stabilised chlorine, and an indoor pool too, so it can't be the sun. What information do I need to add here to help you to help me please? Thanks!

[Denniswiseman]

If you are using stabilised chlorine, then you have CYA and it won't be negligibe. Excess CYA renders your chlorine ineffective
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm
I suggest you get some decent test results even if you have to go to a pool store
FC:
TC:
pH:
TA:
CH:
CYA:

[Eddles]

Hello Denniswiseman, thanks for your reply! I carried out 4 different kinds of testing on the same sample of water. The following list describes my test methods:

Pool store: as described
7-dip: I have dip stripes that gives values of 7 different chemical levels
Disc: I have a BWK145 balanced water kit from Water-ID
SCUBA: I have an electronic pool tester called "SCUBA II"

And here's my results...
- = test not available
? = couldn't match the colour with the key on the packing
x = didn't test

Swimming pool:

Code: Select all

            TH   TC   FC   pH   TA   CyA
Pool store:  -   -   0   6.65   190   -
7-dip        ?   ?   0   7.2   180   30-50
Disc:        -   x   0   7.3   250   -
SCUBA:       -   x   0   7.3   181   >160[1]

Hot tub:

Code: Select all

            TH   TC   FC   pH   TA         CyA
Pool store:  -   -   0   6.9   55         -
7-dip        ?   ?   0   6.2   60         0
Disc:        -   x   0   6.5   70         -
SCUBA:       -   x   0   6.8   175[2]      >160[1]

So now I'm not sure which test method is the most accurate. I've added 1.5 litres TA reducer & 525g chlorine shock to the pool, and 10g chlorine shock, 22g pH increaser & 20ml anti-foam to the hot tub. Will measure FC, pH and TA in the morning. I believe the CyA result from the SCUBA II is accurate as the sample was completely opaque after adding the CyA reagent. Is this my problem?

[1] The SCUBA can't display a figure over 160, it just shows "HIGH".
[2] I think the sample got contaminated at this point.

[Teapot]

Dip strips as you have found are useless especially for CYA. Stop using packaged products as they contain CYA (shock, multi action etc). You could use liquid chlorine or HTH calcium hypochlorite.
You need to empty 50-60% of the water to dilute the CYA. You need some CYA 30-50ppm in most cases but too much and you loose control as you have found. CYA binds chemically to the chlorine, it protects it from the sunlight which burns the chlorine up in a few hours. In your case 99.99% of the chlorine is bound to CYA therefore not enough free available chlorine to sanitise the pool, kill algae etc. Do not go adding algaecide either.

[Denniswiseman]

I second what Teapot says
Your different test results show that the only consistent number is for your pH which is low and acidic
Adding TA reducer reduces reduces your pH as well. Raise your pH first with aeration before reducing TA
Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach)
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA
You really need to get yourself a decent FAS/DPD test kit (Taylor K2006c or TF Testkits TF100 in the states) to get accurate results and control what you are putting in the pool instead of yo-yoing

[Eddles]

Thanks both for excellent advice. Will read and digest all this properly tonight as I'm at work at the moment, but just a couple things before then.

Tested the pool and spa this morning using the BWK kit, pool had 0.2 chlorine, pH 7.3 and TA 230. Spa pH 7.2 and chlorine a big fat zero. Will replace the spa water and start afresh.

As for testing kit, I'm in the UK, is there a good quality equivalent to the test kits recommended?

Many thanks for your time!

[Eddles]

Not yet read fully, but a few more thoughts....

Why am I using stabilised chlorine? I have an indoor pool and hot tub and as far as I'm aware, stabilised chlorine is to prevent the sunlight from messing around with chlorine? Why can't I use unstabilised chlorine?

The SCUBA and BWK kits both use DPD tablets, how would the Taylor or TF kits be better?

Finally, I presume that there is no product that neutralises CyA?

Many thanks again!

[Denniswiseman]

Not yet read fully, but a few more thoughts....

Why am I using stabilised chlorine? I have an indoor pool and hot tub and as far as I'm aware, stabilised chlorine is to prevent the sunlight from messing around with chlorine? Why can't I use unstabilised chlorine?

The SCUBA and BWK kits both use DPD tablets, how would the Taylor or TF kits be better?

Finally, I presume that there is no product that neutralises CyA?

Many thanks again!

You don't need stabilised chlorine but it is suggested that indoor pools have about 20-30 (I have an indoor pool)
I have already previously suggested the products to use but you can use your tablets to back up when your CYA gets low (backwash and spill out)
I'm not familar with the SCUBA and BWK kits, Teapot may be able to help better (I got my Taylor from the states)
You are correct there is no product that neutralises CYA except time

[Eddles]

Hello both, thanks for advice! Now I've had a bit of time to fully read what you both have said. I'm definitely going to move to unstabilised chlorine (with stabilised chlorine as backup if CyA goes down), however liquid chlorine scares the bejesus out of me. Looking on HTH's website, they sell to industrial/commercial customers, however they re-package their products as Fi-Clor for the residental market. Looking on Fi-Clor's website, it seems that the best way would be to use their 300g tablets put in the skimmer basket for the swimming pool. However, I can't find unstabilised chlorine for hot tubs? Or should I just continue with stabilised chlorine and change water when CyA goes too high?

Then from your recommended list, get/do the following:

• 300g unstabilised chlorine tablets
• Unstabilised chlorine shock
• Taylor K2006C test kit (where to get replacement reagents for this, though?)
• Build an aeration system.
  In addition, I already use the following chemicals, are they OK?
• Sodium Bisulphate pH reducer.
• Sodium Carbonate pH increaser.
• Sodium Bicarbonate TA increaser.
• Soda ash to raise pH & TA (never used this though).

Then, junk everything else (e.g. TA reducer, oxyshock, non-chlorine shock, etc) that's not for maintenance (e.g. waterline cleaner, antifoam, etc)? I've never used algaecide and haven't needed flocculants for a while.

For now, I'll drain the pool halfway and hopefully CyA will go down to a more reasonable level. Also... How do I safely change in between unstabilised and stabilised chlorine? Do I just make sure the skimmer is clean before changing over, or do I need to rinse it or something?

Many thanks for your time!

[Denniswiseman]

First of all liquid chlorine is sodium hypochlorite or plain bleach not the thick or scented, if you use bleach in the house you can use plain bleach in the pool
Shock is just a large dose of chlorine
Unstabilised chlorine shock has calcium in it which can lead to calcium build up in the pool
Fi-Clor has calcium in it
Now Hydrochloric acid (Muriatic acid) is noxious but highly effective, however dry acid (sodium bisulfate) will lower both pH and TA. You should then aerate to bring your pH up again
There is no procedure for changing from stabilised chlorine to unstabilised, just pour sodium hypochlorite or plain bleach in front of a return
Your shock and chlorine level is determined by your CYA level Chlorine / CYA Chart

[Eddles]

Ah, drat, yes that makes sense! It's not as easy as it looks! OK, I'll get liquid chlorine, hopefully when I report back in a couple weeks time, the pool will be perfect!

How do I use liquid chlorine with the hot tub? The swimming chemicals websites says they're not suitable for hot tubs? Can you advise please?

Many thanks for your time and fantastic advice!

[Eddles]

I'll also need a respirator. What kind of respirator do I need to look for please?

Many thanks!

[Denniswiseman]

I'll also need a respirator. What kind of respirator do I need to look for please?

Many thanks!

What do you need a respirator for, sodium hypochlorite/bleach isn't noxious or did you mean aerator
You can use liquid chlorine for the spa but you may need to add CYA to buffer the chlorine or use trichlor/dichlor (types of stabilised chlorine) to add the CYA

[Teapot]

I would advise buying a low cost chemical dosing pump. Depending on the amount of sunlight your indoor pool gets as to CYA or not. You can with zero CYA run at 0.2-0.5ppm of chlorine.

[witters]

Apologies if this is against protocol, but rather than starting a new thread could I, please, ask the same question?
I, too, am suffering from an excessive, apparently ineffective use of large quantities of chlorine.
Over the past couple of weeks I have brought down the TA from 245 to 175 (still high, I know, but my fill water is very alkanine) and reduced the pH from 8.0 to a consistent 7.5. I've used 23% Hydrochloric Acid from the Brico to do this. Calcium Hardness is a consistent 190 - 200 throughout all tests. CYA is also consistent at an average of 35.
The water is crystal clear, the vinyl is cleaned to within an inch of its life and debris is vacuumed to waste.
My problem is that I can't maintain an adequate chlorine level - it just seems to disappear. The solar cover is on most of the day since the pool, at the moment, is only used for short periods. For chlorination I use 9.6% Javel.
Recent Chlorine readings are as follows:
Wednesday evening Cl 0.47, TCl 1.99 so I added shock quantities 5 litres bleach to try and eliminate the Combined Chlorine (the dose should have added 16ppm for my size pool)
Thursday morning Cl 0.26, TCl 0.69
Checked to eliminate DPD bleaching by diluting sample with distilled water - same results (pro-rata)
Midday Thursday, added 250g Chlore Rapide 60 (since I'd run out of Javel) Troclosene Sodium Dihydrate, theoretically enough to reach shock level.
6 pm Thursday, Cl 0.12, TCl 0.45.
These are the most recent readings (I use LaMotte ColorQ). Over the past ten days I have used 20 litres of 9.6% bleach without going above 2 ppm FCl. Prior to acid treatment when pH was 8.0 and TA was 245 I was getting Cl and TCl of 5.5. After reducing pH and Alk I am struggling to keep any chlorine.
I would appreciate any suggestions. I am at my wit's end. What alien life form is eating my chlorine? Would phosphate remover help? Is there anything else, unseen, that could be eating away at all the chlorine I'm throwing at the pool? Pool is 32,000 litres, currently at 26 degrees, vinyl lined, half outside (with solar cover), half inside, 3 returns and a skimmer on the outside, 3 returns and a skimmer on the inside, all circulation through a single pump and glass filter.
Thank you in advance