Consistently low pH

[Sandybits]

Hi,
I am trying to help my brother in law with his pool but it has me stumped as his chlorine is consistently low as is his pH.

It's a 17000 gallon concrete in ground pool that has been resurfaced with fibreglass. He runs a 1 HP pump, 25 gram chlorinator and sand filter. The chlorinator is running 10 hours at 100%. It's in a subtropical area.

From the pool shop:
Fcl 0.81
pH 6.5
All 43
Hard 0
Cya 60
Phosphate 1400
Salt 4700

The problems:
* The system is struggling to produce enough chlorine. Visible gases coming off plates and plates are clean in cell.
* The pH is consistently this low (over the past tests that he had kept) even though he's running a salt water chlorinator which should push pH up.
* The calcium is being lost as the low calcium results are consistent even after balancing. He put several kgs in about 2 months back.

Our guesses:
* Filtration is slightly undersized for the pool. The furthest jet from the pump house barely moves any water this low chlorine.
* He runs his roof water into the pool and it was repainted a year ago maybe altering the pH.

It just seems unusual to have consistently low ph when running a salt water chlorinator.

Any ideas? Thanks.

 

[mknauss]

Welcome to the forum! :handshake:

I assume he does not have access to his own test kit? CYA is a necessary chemistry result to assist. Also you can raise pH, raise the TA by adding baking soda.

The FC is being consumed by either the sun (low CYA) or organics. If organics, he will need a proper test kit to do a Overnight Chlorine Loss Test and most likely a SLAM Process.

I suggest you read Pool School - ABCs of Pool Water Chemistry and consider reviewing the entire Trouble Free Pool School book.

 

[jblizzle]

Welcome to TFP!!!

How much water is being diverted into the pool? Only way for the CH to drop is through the addition of a lot of water with low calcium levels.
For example, if they had a leak and were constantly refilling with very soft water.

What is the pH and TA and CH of the fill water out of the tap?
Perhaps test the same on the water coming off the roof.

Really need their own test kit for us to be able to further help.

 

[Sandybits]

Thanks Marty, I edited post to add cya. I overlooked it.

I will go back over those links you suggested.

The real brain scratcher was the consistently low ph even though running a salt water chlorinator which traditionally pushed pH up over time. I can't seem to figure that bit out.

 

[mknauss]

A SWCG does not push the pH up if the water chemistry conditions do not warrant it. With low TA your pH will not increase rapidly.

He should add 30 ppm worth of baking soda. Then see what the pH is the next day.

 

[Sandybits]

Welcome to TFP!!!

How much water is being diverted into the pool? Only way for the CH to drop is through the addition of a lot of water with low calcium levels.
For example, if they had a leak and were constantly refilling with very soft water.

What is the pH and TA and CH of the fill water out of the tap?
Perhaps test the same on the water coming off the roof.

Really need their own test kit for us to be able to further help.

His pool is always full, even above the skimmer. And most of that fill water is from rain.

I'll see if we can test the roof runoff and I'll encourage him to get a decent test kit.

Thanks.

 

[mknauss]

What country is he in?

 

[Sandybits]

A SWCG does not push the pH up if the water chemistry conditions do not warrant it. With low TA your pH will not increase rapidly.

He should add 30 ppm worth of baking soda. Then see what the pH is the next day.

I thought low TA caused swings in ph but never considered that just having unbalanced TA would do the same. That would make sense in his case.

I'll tell him to get some bicarb and get the TA up. Thanks Marty.

- - - Updated - - -

What country is he in?

Up the road from me in Australia. Need to update my sig

 

[mknauss]

Then both of you need a test kit from ClearChoice Labs -- http://www.clearchoice.labs.com.au/

 

[Sandybits]

Then both of you need a test kit from ClearChoice Labs -- http://www.clearchoice.labs.com.au/

Done.

4 kg (1.8 lbs,?) Of Buffer is in the pool.

The roof runoff isn't the problem as it hasn't been diverted in to the pool for months.

 

[mknauss]

Sounds good. Have him circulate that for a day and test pH and TA.