Alkalinity Testing Inconsistency

[ScoobyDoo]

I recently stumbled across this site and love it. I have a 3 month old SWG gunnite pool. I'm not exactly sure what volume it is but based on some recent conditioner addition, I'm estimating its 20,000 gal. I've read all about the BBB method and I'm slowly moving my pool that direction. Truly, I wish I had run across this sooner as my alkalinity was perfect range but I added quite a bit of baking soda to get my alkalinity numbers up as I believed higher alkalinity 100+ ppm was disireable.

My pool is consuming an incredible amount of acid to keep the pH in check. Haven't exactly been measuring the amount but I've got access to industrial strength MU (37%?) and I've added 2 gallons of it over the last 6 weeks to keep the pH in check. I had a saltwater pool at my last house, it was also a 3 year old gunnite pool, and the acid consumption was significantly lower with 30% acid. Is that because the gunnite was fully cured?

I have a Oreq deluxe test kit I'm using to monitor chlorine, pH, and alkalinity and I'm using Leslies to help with CYU and CH. FC has been probablematic keeping in check so I suspected my CYU was low so I got my pool were I thought it should be and took some samples into the Leslies. The first Leslie's was out of reagent so I took the same sample to a second store and had them run as well. Based on yesterday's results, my conditions were-

My results Leslie's Store 1 Leslie's Store 2
FC 4, 4, 4
pH 7.6, 7.4, 7.8
TA 150, 100, 80
CYU -, 35, 40
CH -, -, 300
Salt -, 3400, -

So I bought a gallon of conditioner to bump up my CYU and put the whole thing in. Today, my results are -

My results Leslie's Store 1
FC 3-4, 3
pH 7.5, 7.8
TA 130, 80
CYU -, 50
CH -, 350
Salt -, 3900

I'm working on trying to bring my alkalinity back down so I added another 1/2 gallon of MU this afternoon and turned on my sheer descents. An hour later, I've measured a pH of 6.8 and a TA of 110 ppm. I can see it is going to take a while to bring my TA in range.


So questions -

1. I'm using an Oreq deluxe test kit(came with the pool) to monitor FC, pH, and TA. I'm concerned with the wildly different numbers I'm getting between the pool stores and myself. Is the Oreq kit reasonably accurate to trust over the pool stores? I know the forum recommends the expensive kits but I would think that once CYU is set at the recommended levels, its not a test I need to monitor closely and can get that run at the pool stores from time to time. Same with CH.

2. I'm normally measuring water levels about an hour after additions. This may tie into question 1 but is that too soon to get a stable reading or is just fine? In both cases, I did my measurements an hour after additions and took a sample to Leslie's.

3. Is the high acid consumption (which seems to me excessive) normal for a new pool?

4. Is there a cheaper source for CYU? Paying $37 for a gallon of Natural Chemistry Conditioner @ Leslies.

 

[wetwilly]

I'm not experienced enough to tackle 1-3, but regarding #4: You should be able to purchase 5lb of Conditioner (Cyanuric Acid) granules for about $20 at Home Depot. BTW: It is CYA not CYU.

Just be careful adding it. Too much is a bad thing and after adding, it takes a week to show up on test results. Be sure to read pool school too.

I hope this helps.

- Bill

 

[JasonLion]

1) That isn't one of the kits we recommend. While it can give you numbers that are better than what many pool stores can do, it won't be as reliable as the better test kits. Everything depends on having reliable test results. If you don't know what is going on in the water there is no way to treat it properly and you will end up wasting time and spending more money fighting the wrong problems because you have the wrong numbers.
2) Waiting one hour with the pump running is fine for most chemicals. CYA and salt are the main exceptions. CYA requires a week, and salt 24 hours.
3) Yes. Fresh plaster will raise the PH, TA, and CH levels quite quickly for the first three or four weeks, and more slowly for up to a year. You need to keep control over the PH or you are likely to get calcium scaling.
4) The liquid CYA/conditioner is by far the most expensive form of CYA. Granular is about half the price.

 

[ScoobyDoo]

Thanks. I am sure I'll end up buying the better test kit. But I also have to point out I used this same kit on my last saltwater pool and both pools had/have clear water. I'll admit tho, my last pool, when the water got fairly warm (90F !!!), had a spout of black algae. Leslie's gladly sold me some phosphate remover and algaecide.

I read the pool school but I still don't quite understand why lower alkalinity levels are recommended for saltwater pools. Could you explain rational. I was under the impression higher alkalinity = bigger buffer which resisted changing pH.

 

[JasonLion]

High TA does two unrelated things. First it buffers PH changes, so it takes more to shift the PH. And second, higher TA puts upward pressure on the PH, so that PH drifts up slowly, more quickly the higher the TA. How quickly the PH actually drifts depends on a number of factors, one of the larger of which is the amount of aeration the pool is getting. A standard pool gets very little aeration (unless there are lots of kids swimming), but a SWG produces lots and lots of tiny bubbles, which are quite effective at aerating the water.

To sum up, more PH drift at higher TA. More PH drift at lower PH. More PH drift with more aeration.