Can't lower pH

[BillB]

FC - 7.0
pH - 7.8
TA - 120
CYA- 50
Borate - 50


My TA was down around 60, so I added 8 lb of baking soda, yesterday.
I waited 3 or 4 hours and it read 130.
My pH was up around 8.0 so I added 1 qt +3 oz. of muriatic acid. That was 1/2 of what the pool calculator gave to lower pH to 7.2.
Checked it about an hour later. pH read 7.7 (Guessing at colors), so I added the other quart of acid.
That was about 2 hours before I turned the pump off.

I ran it about an hour this morning and pH still reads 7.7 or 7.8.

I hate to keep pouring acid into what looks like illogical readings. Should I hit it with another quart or wait awhile and check it?

Thanks

 

[tim5055]

What test kit are you using? You can add that to your signature so we are sure when we answer.

Could your FC actually be above 10 and you are getting false high pH? Is there a lot of kids splashing around or a fountain or other water feature running?

The baking soda would push up the pH a little, and now your TA is a little higher than it should be.

For your pool you want:
with Bleach
FC 3-7 (See chart)
pH 7.5-7.8
TA 70-90+
CH 250-350
CYA 30-50

 

[BillB]

TF-100
There is nothing going on with the pool- no one in it- no aeration.

I'll retest the FC.

 

[BoDarville]

The pH scale is logarithmic, not linear. Each one full point change (e.g., 7.0 to 8.0) on the pH scale equates to a 10X change in the acidity/basicity. In other words, if pH is sitting at 8 and you are targeting a pH of 7.6, you cannot assume that adding half the amount of MA needed for a pH of 7.2 will result in a pH of 7.6. The PoolMath tool accounts for this logarithmic scale.

In addition, as you add muriatic acid (MA) to lower pH, the TA will also drop. This means that you will need to add less MA to reach your target pH with each subsequent addition. Since MA affects two parameters (pH and TA), you will need to retest both of these before adding MA. Enter your test results in PoolMath to get the proper dosage.

Another thought...When dosing FC to reach a target, does the dosage stated by PoolMath enable you to hit your target? If not, then your pool volume may differ from what you think it is. If this is the case, it would impact other dosage amounts.

 

[JasonLion]

How old is your plaster? Fresh plaster will raise the PH rapidly for the first month or so.

 

[BillB]

What test kit are you using? You can add that to your signature so we are sure when we answer.

Could your FC actually be above 10 and you are getting false high pH? Is there a lot of kids splashing around or a fountain or other water feature running?

The baking soda would push up the pH a little, and now your TA is a little higher than it should be.

For your pool you want:
with Bleach
FC 3-7 (See chart)
pH 7.5-7.8
TA 70-90+
CH 250-350
CYA 30-50

FC is 4-8 for 50 CYA per the pool calc.

- - - Updated - - -

How old is your plaster? Fresh plaster will raise the PH rapidly for the first month or so.

Plaster is 17 years old.
I readjusted my return jets yesterday and just noticed that 2 of them are causing slight ripples in the water. I don't think it's enough to cause what I'm experiencing but I will readjust them