ph keeps returning to 6.5

my chlorine pool ph keeps returning to 6.5! At the beginning of summer when the pool water was around 30ºC I noticed the ph had dropped rapidly to 6.5. I added borax to raise it. It raised to 7.6. After 15 days it returned to 6.5. I added a fountain to one of my return jets. With the pump on 10 hours a day the fountain does nothing to raise the ph. Anyone have any ideas why?
I added borax again and brought the ph up to 7.4 and again after 14 days it sunk back down to 6.5 again.
The TA is high. It changed every day, but is between 140 and 180.
I am using chlorine tablets that are sold as 'slow' chlorine with cyanuric acid added. Once a week after vacuuming and backwashing I shock the pool with rapid chlorine.
The pool water is constantly between 29ºC and 31ºC since the end of June.

Any help would be appreciated!
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
It is the tablets that are crashing the pH ... it is surprising that the TA is also not dropping (unless your fill water has high TA).

What are you testing the water with?
And like James asked, what is your CYA level up to now? Are you keeping the FC above the minimum for your CYA according to the [FC/CYA][/FC/CYA] at all times?
 
It is the tablets that are crashing the pH ... it is surprising that the TA is also not dropping (unless your fill water has high TA).

What are you testing the water with?
And like James asked, what is your CYA level up to now? Are you keeping the FC above the minimum for your CYA according to the [FC/CYA][/FC/CYA] at all times?
I'm new to all this. I'm testing my water witha digital reader called aquacheck. It gives me the readings for chlorine, ph and total alkalinity.

I inherited the pool with the house I bought 3 years ago. I followed the previous owner's advice for the pool maintenance and for the past 3 years the readings were all ok on aquacheck. Except when I had some problems with high ph readings in the first summer and used muriatic acid to lower it.

On the pool shop guy's recommendation in May of this year I started using tablets with a ph stabliser and algicide in them. It was in late June this year that my ph dropped, so I figured it was these new tabs, so I changed back to simple slow chlorine tabs.
 

Spa Owner

In The Industry
Jul 14, 2017
162
Victoria Park, Antipodean
I'm new to all this. I'm testing my water witha digital reader called aquacheck. It gives me the readings for chlorine, ph and total alkalinity.

I inherited the pool with the house I bought 3 years ago. I followed the previous owner's advice for the pool maintenance and for the past 3 years the readings were all ok on aquacheck. Except when I had some problems with high ph readings in the first summer and used muriatic acid to lower it.

On the pool shop guy's recommendation in May of this year I started using tablets with a ph stabliser and algicide in them. It was in late June this year that my ph dropped, so I figured it was these new tabs, so I changed back to simple slow chlorine tabs.
Try a different test kit. The Aquacheck is a strip reader and test strips are notoriously unreliable.
 

domct203

Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
3,959
CT
I'm new to all this. I'm testing my water witha digital reader called aquacheck. It gives me the readings for chlorine, ph and total alkalinity.

I inherited the pool with the house I bought 3 years ago. I followed the previous owner's advice for the pool maintenance and for the past 3 years the readings were all ok on aquacheck. Except when I had some problems with high ph readings in the first summer and used muriatic acid to lower it.

On the pool shop guy's recommendation in May of this year I started using tablets with a ph stabliser and algicide in them. It was in late June this year that my ph dropped, so I figured it was these new tabs, so I changed back to simple slow chlorine tabs.
You really do not have a proper testing kit. Not only are test strips unreliable, you are only checking a couple of parameters of the pool chemistry. We need to know:
FC
CC
pH
TA
CH
CYA

I’ve never heard of ‘pH stabilized chlorine tablets’. What was the exact brand? It would be helpful to know exactly what they were adding to the pool. I’m guessing copper (sulfate) is the algaecide, which you do not want in the pool.
 
You really do not have a proper testing kit. Not only are test strips unreliable, you are only checking a couple of parameters of the pool chemistry. We need to know:
FC
CC
pH
TA
CH
CYA

I’ve never heard of ‘pH stabilized chlorine tablets’. What was the exact brand? It would be helpful to know exactly what they were adding to the pool. I’m guessing copper (sulfate) is the algaecide, which you do not want in the pool.
Thanks for all the information. I'll look around to get a quality testing kit that measures all those qualities you mention. I may have to send off for one online, as I've never seen a kit that is so comprehensive in the pool supply shops here.

The name of the chlorine tablets with the ph stabiliser and algicide is Aquapool compacta multi-accione tabletas discount pool supplies.
the ingredients are symclosene, aluminium sulfate, boric acid.

The name of the tablets without ph stabiliser and algicide is Aquapool tabletas cloro 200g.
The ingredients are symclosene, boric acid.
 

trivetman

Bronze Supporter
Jul 14, 2017
306
Jenkintown, PA

Spa Owner

In The Industry
Jul 14, 2017
162
Victoria Park, Antipodean
Thanks for all the information. I'll look around to get a quality testing kit that measures all those qualities you mention. I may have to send off for one online, as I've never seen a kit that is so comprehensive in the pool supply shops here.

The name of the chlorine tablets with the ph stabiliser and algicide is Aquapool compacta multi-accione tabletas discount pool supplies.
the ingredients are symclosene, aluminium sulfate, boric acid.

The name of the tablets without ph stabiliser and algicide is Aquapool tabletas cloro 200g.
The ingredients are symclosene, boric acid.
The tablets are isocyanuric based chlorine one with floc in the other without. There is no discernible difference between the two products.

The tablets are lowering the pH of the pool. They have too. Its part of their chemistry, and are not pH stabilised. Something else not that it matters I don't understand how they are claiming the algicide properties in the second tablet. It doesn't contain an algaecide unless they are simply playing with the wording (common for chemical companies) as chlorine is an algaecide.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,318
Laughlin, NV
Boric acid is a sort of algaecide.

It will build up in your water just like cyanuric acid. Pucks are not for long term use.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
20,412
Northern NJ
https://www.troublefreepool.com/content/124-pool-test-kits-comparison

people on this site swear by the TF-100. Taylor K-2006/2006C is also a good option. Both give all the tests results which Dom listed.
Note the OP is in Spain and does not have easy access to the test kits we have in the USA.

We have to work with her with what she has available.

Elaine, you have to move from using the tablets to chlorinating your pool with liquid chlorine/bleach. Bleach has to ne unscented with no additives. You will need to find sources for it and what % chlorine you can get.

We have lots for you to read at Pool School - Pool School Please read:
Pool School - ABCs of Pool Water Chemistry
Trouble Free Pool School
Pool School - Recommended Pool Chemicals
Pool School - How to Chlorinate Your Pool
Pool School - Basic Pool Care Schedule
Pool School - Test Kits Compared
 
The tablets are isocyanuric based chlorine one with floc in the other without. There is no discernible difference between the two products.

The tablets are lowering the pH of the pool. They have too. Its part of their chemistry, and are not pH stabilised. Something else not that it matters I don't understand how they are claiming the algicide properties in the second tablet. It doesn't contain an algaecide unless they are simply playing with the wording (common for chemical companies) as chlorine is an algaecide.
Thank you all so much for all your help.

I have spent the whole day looking online for the recommended pool test kits and can't find anyone supplying them in Spain and because of regulations they can't be shipped here either :(
I'm looking now to see if I can find one that tests for as many of the necessary readings as possible. Most just measure for ph and chlorine. There are some strips that measure for CH and CYA as well. Would strips be better than nothing? Or are they so unreliable that it isn't worth getting them?

mknauss, jblizzle and Spa Owner, It all makes sense now that you've explained it to me. The cyanuric acid in the tablets is an acid and of course would lower the ph.

Allen, I can look around for liquid chlorine/bleach. I know they sell unscented/unadulterated bleach at my supermarket. it has 37gramms of sodium hypochlorite per litre.
And I can check in the pool shop if they have a stronger solution for the pool.

I feel such a relief now that I'm getting some answers.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
I would not bother with the strips. I remember there was a kit over there that was roughly equivalent to the Taylors .... let me search the forum a bit

- - - Updated - - -

See if anything of these leads help:
Test kits in europe

There is one specifically for spain/portugal

- - - Updated - - -

Here is another reference to it:
Taylor k-2006 in Mucia Spain
 
Note the OP is in Spain and does not have easy access to the test kits we have in the USA.

We have to work with her with what she has available.

Elaine, you have to move from using the tablets to chlorinating your pool with liquid chlorine/bleach. Bleach has to ne unscented with no additives. You will need to find sources for it and what % chlorine you can get.

We have lots for you to read at Pool School - Pool School Please read:
Pool School - ABCs of Pool Water Chemistry
Trouble Free Pool School
Pool School - Recommended Pool Chemicals
Pool School - How to Chlorinate Your Pool
Pool School - Basic Pool Care Schedule
Pool School - Test Kits Compared
I would not bother with the strips. I remember there was a kit over there that was roughly equivalent to the Taylors .... let me search the forum a bit

- - - Updated - - -

See if anything of these leads help:
Test kits in europe

There is one specifically for spain/portugal

- - - Updated - - -

Here is another reference to it:
Taylor k-2006 in Mucia Spain
Thank you for the links for the pool tester. I'll check them out.

I found liquid chlorine/bleach at the tractor & supply store. It is 14%.

I removed the tabs I had in the water, added borax to bring the ph up to 7.4 and have put in the bleach in and have the chlorine levels at 2 at the moment.
Will the cyanuric acid that is left in the water as residue from the tabs help to stabilise the chlorine/bleach I added?
I have no idea what the CYA levels are because I'm still working with a tester for chlorine, ph, and total alkilinity only...