Confused about alkalinity and pH

[tlevy]

So I have a slightly low alkalinity level - last test was about 80 ppm. Latest test results are:

FC 4
CC 0
pH 7.5
Calcium 200
Alkalinity 80
CYA 70

I think need to bump my alkalinity up, so planning to add some arm and hammer shortly, to move it closer to about 95-100 ppm. Won't that throw my pH off though? Then I would add some muriatic acid, but won't that then drop my alkalinity back down again?

#confused

 

[Griswald]

Why do you feel the need to change the TA?

I'd be more concerned with your free chlorine level at 4 with 70 CYA, you need at least 6.

 

[lightingguy]

What kind of pool do you have? Vinyl or Plaster?

If your PH is stable I wouldn't change the TA. If you have a plaster pool you might want to add some calcium.

 

[kabutotx]

TA is sometimes called a buffer. It is there to help your pH from changing much. To low TA and you get quick pH changes. Too much and pH keeps raising itself. Get as much or little as needed for YOUR pool. A person with a SWG or operating water features will have different requirements than someone without etc.

 

[tlevy]

Why do you feel the need to change the TA?

I'd be more concerned with your free chlorine level at 4 with 70 CYA, you need at least 6.

Understood. Will bump SWG output to 50%.

On the alkalinity, it was my understanding I am on the low end. But...if y'all think it is good, then I will go on this.


68,000litre, IG vinyl, LorentzPS 600 Solar Pump & 1/2 HP Tristar, Sandfilter, Aquarite T-15 SWG

 

[tlevy]

What kind of pool do you have? Vinyl or Plaster?

If your PH is stable I wouldn't change the TA. If you have a plaster pool you might want to add some calcium.

Vinyl


68,000litre, IG vinyl, LorentzPS 600 Solar Pump & 1/2 HP Tristar, Sandfilter, Aquarite T-15 SWG

 

[tlevy]

I typically add acid weekly or every ten days to keep it in the sweet spot. I don't think it swings too much, just a slow rise over a short period, which I understand is typical of SWG pools...


68,000litre, IG vinyl, LorentzPS 600 Solar Pump & 1/2 HP Tristar, Sandfilter, Aquarite T-15 SWG

 

[wayner]

Isn't the recommendation for TA to be from 60-80? Therefore you are more on the high side than the low side, according to here: Pool School - Recommended Levels

I have a SWCG as well and I have always been fine running my FC closer to the minimum than the recommended levels. For CYA of 70 the min is 5 and the recommended is 8.

Maybe I am wrong on this but I think those of us in cooler places with seasonal pools in places like Canada have less issues with algae and can live with lower FC, especially if your water is cooler.

 

[lightingguy]

Here we advise a lower TA because the types of chlorination we recommend tend to raise PH over time.

If you were using TriChlor pucks you would want a higher TA as Trichlor is acidic.


If it were me I would lower the TA to see if I could cut the PH rise down. You don't need to do this - it's just about convenience.

 

[Schadenfreude]

No, for CYA of 70 with a SWG, the recommended min FC is 3 with a target of 5 - see here.

If your Ph is not rising too quickly, your TA is fine - if it does, then you can lower your TA to 70 and see if that helps. All of your other numbers look fine, too. You have a vinyl liner, so don't worry about CH.