extreme TA drop, is this even possible?

[mknauss]

Correct.

 

[crackers8199]

Correct.

Great. I'll hold off doing anything on that front then until I get my test kit in hand and can test the alkalinity myself.

Would you suggest I wait til tomorrow to add acid and see what the rise is after one more day, or add acid now to bring it back down into the low to mid 7s? Or even wait until it gets up to 7.9 or 8.0+ before adding acid?

I'm guessing I don't want to let it drift up to 8.0 or above, but I'm trying to figure out the optimal time to add acid to bring it back down...

 

[mknauss]

When pH reaches 8, lower to 7.6. You need a decent TA number for PoolMath to calculate how much acid to use.

 

[mgtfp]

Today pH reads 7.7 (so only up 0.1 since yesterday morning). Safe to say the TA can't possibly be that low if pH is reasonably stable like this (as you were saying earlier)?

Be careful not to confuse two effects of TA:

On one hand, you need a certain TA-level so your pH doesn't fluctuate wildly. The chlorination process itself (either by SWG or by adding bleach or cal-hypo) rises pH. The subsequent use of chlorine (either by UV-destruction or the actual use as an oxidizer/sanitizer) brings the pH back down, this is a kind of a closed loop, as long as you only add enough chlorine to compensate the daily losses, the pH remains constant within this up-and-down cycle. You need a certain TA-level to keep this daily up-and-down cycle within acceptable limits. This is the intended function of adding baking soda to your pool as a buffer. In the same way, high TA will buffer the effect of adding muriatic acid. When adding m.a. to lower your pH, you have to add more when you have high TA to get the same effect on pH.

On the other hand, you have a side effect of TA, that leads to a constant rise of pH: The higher your TA is, the more CO2 you have dissolved in your water. The water is trying to reach an equilibrium where the same number of CO2 molecules leave the water as come back from the atmosphere into the water. That means that at high TA levels, there is a constant out-gassing of CO2 happening which effectively raises the pH. You see this particularly with SWGs, because the SWG process creates hydrogen bubbles. As these bubbles contain only hydrogen (i.e. no CO2), CO2 from the water will very quickly evaporate into these bubbles, driving your pH up over time. But any type of aeration (water features, kids splashing, the constant air volume sitting over your pool, ...) results in CO2 out-gassing. That's why TFP recommends lower TA levels compared to the standard pool industry advice.

That second aspect is what Marty was referring to when he said "If your pH rose by 0.3 in a day, your TA is not low". 0.3 is quite a lot for one day. Even 0.1, I still consider quite a lot for one day, indicating that your your TA should be quite high. But not because "pH is reasonable stable" as you concluded, but because 0.1 is still a considerable drift for just one day. On the other hand, 0.1 is still quite low to actually see a difference in colour in the pH test, so you needed to watch that over a longer period to work out the average daily drift.

You need to find that sweet spot with the right TA for your pool, where your daily pH-fluctuations are small (buffer function of TA), long-term pH rise is small (CO2 out-gassing due to high TA) and your CSI is in the desired range where you don't get scaling or plaster damage (higher TA means higher CSI).

When you compare measurements from one morning to the next morning (i.e. at the same points within your cycle of chlorine use and creation), you would primarily see the steady pH-rise due to CO2 out-gassing. Small rise from morning to morning means TA should not be too high.

If you do multiple measurements during the day and you see a wild up and down, then you'd see the effect of TA being too low. You shouldn't see that effect with a colour based test at all, you'd need a high quality, high precision test for that, unless the TA is really that low. But you really needed to see a significant up and down around the steady pH-rise to conclude that your TA is too low.

 

[crackers8199]

But not because "pH is reasonable stable" as you concluded, but because 0.1 is still a considerable drift for just one day.

...

When you compare measurements from one morning to the next morning (i.e. at the same points within your cycle of chlorine use and creation), you would primarily see the steady pH-rise due to CO2 out-gassing. Small rise from morning to morning means TA should not be too high.

i was under the assumption that because i have a spillover that is running for around 10 hours a day (3 of which are with the pump on high speed and a good deal of aeration), i'm always going to have some drift upwards. are you saying even with that i should be aiming to have it staying constant over a period of a few days?

today's reading was 7.8 by the way, so up another 0.1.

 

[mgtfp]

You are right there, there will always be aeration driving pH up. I only wanted to point out that this drift is larger with higher TA. There is more CO2 in the water at higher TA to out-gas. It is not the stabilising effect of TA that reduces the drift, but the higher CO2 in the water at higher TAs that increase the drift. You can minimise the drift by having TA not too high. 0.3 per day is certainly a lot. 0.1 still sounds on the high side, but might be what's required for your pool. Important is to test TA with the kit you ordered, then we'll know if the drift can be reduced.

 

[crackers8199]

You are right there, there will always be aeration driving pH up. I only wanted to point out that this drift is larger with higher TA. There is more CO2 in the water at higher TA to out-gas. It is not the stabilising effect of TA that reduces the drift, but the higher CO2 in the water at higher TAs that increase the drift. You can minimise the drift by having TA not too high. 0.3 per day is certainly a lot. 0.1 still sounds on the high side, but might be what's required for your pool. Important is to test TA with the kit you ordered, then we'll know if the drift can be reduced.

10-4. i'll report back as soon as i have my kit in hand and can test the TA (and the pH for that matter as well) manually myself.

 

[crackers8199]

got notification that my kit was shipped, should hopefully be here thursday...but i wanted to report back because it intrigued me: pH reading from the waterguru was 7.8 again this morning (so completely stable from yesterday).

i know we will find out more once i can run the battery of tests from the TF-100, but is it possible that the equilibrium point would be something as high as 7.8 or is it likely we'll try to adjust that down once we have a full picture?

 

[mknauss]

A pH of 7.8 is much closer to what water has as an equilibrium. If the TA is in the 70 range, that could be a place it settles. Though you will be adding fill water due to evaporation and most likely that fill water has a higher TA.

 

[crackers8199]

A pH of 7.8 is much closer to what water has as an equilibrium. If the TA is in the 70 range, that could be a place it settles. Though you will be adding fill water due to evaporation and most likely that fill water has a higher TA.

i'm ok to leave it at 7.8 for now though and not add acid until it drifts up to 8 though, right? at least until we figure out what the TA actually is...

 

[mknauss]

A high pH only really effects the scaling tendency. So if your IC40 starts to shed calcium flakes, then lower the pH to 7.6.

 

[crackers8199]

A high pH only really effects the scaling tendency. So if your IC40 starts to shed calcium flakes, then lower the pH to 7.6.

haven't seen any flakes coming off yet, but scaling is a concern. there's already significant buildup on the faux rocks around the waterline that i'm getting estimates on having stripped / cleaned and repainted...so i want to make sure i keep it from scaling in the future once i have that done.

that being said, i don't know what the previous water conditions were to cause that scale...so it's possible it was left to sit higher than 7.8 for extended periods.

 

[mgtfp]

that being said, i don't know what the previous water conditions were to cause that scale...so it's possible it was left to sit higher than 7.8 for extended periods.

It's not just pH. If your CH and TA was very high, then scaling can occur already at lower pH. Play around with the numbers in PoolMath and see what the effects of the water parameters (including temperature) on CSI are.

I think Marty wanted to particularly point out, that in a CYA stabilized pool, high pH won't have much impact on the sanitizing effects of chlorine (which is what the pool store will make you think to sell more muriatic acid and overpriced baking soda once all that m.a. has driven down your TA). The only potentially harmful effect of high pH with TFP recommended CYA levels and matching FC levels is scaling. Which exact pH is critical, depends on your water parameters, especially CH and TA. But temperature also has a big impact. 90F summer water is very different to 45F winter water. Of course, once pH is too high, you will also notice other effects like stinging eyes - but not at 7.8.

 

[crackers8199]

Well, test kit will be here tomorrow but I need to get better at guesstimating the amount of acid I'm adding. I way overshot it again yesterday and dropped it from 7.9 to 7.1.

 

[mgtfp]

Part of that is probably that the numbers you put into PoolMath to calculate how much acid to add are not correct.

The pH calculations are quite complex, multiple equilibriums to consider, there is not a simple analytical equation. PoolMath uses an approximation, it usually gives a good guess, but the larger the pH change, the bigger the error will be. For a perfect calculation you need complex (and expensive) chemical equilibrium simulation tools. And precise values for the water parameters.

It is good practice not to add larger amounts of muriatic acid (that actually applies to all chemicals) in one go. Add half first, test after a while and decide how much more to add. Over time you will learn how your pool reacts to chemical additions. And always use results from your test kit to calculate how much of a chemical to add.

 

[crackers8199]

alright, here's my first set of numbers with the TF100:

Results from poollogger.com

FC: 6.5
CC: .5
PH: 7.2
TA: 60
CH: 1225
CYA: 60
CSI: -0.92

the CH number i'm not entirely sure i did right...i know we have extremely hard water, but i felt like if i looked at the tube at a certain angle it looked blue, but the actual meniscus didn't turn blue until drop 49. i guess i'll get better with this as i go...same for CYA.

PH is pretty much right on with what the waterguru told me this morning (WG said 7.3). FC is higher (WG said 3.5)...which seems to be in line with what other reports i've seen on the waterguru have said. PH is pretty accurate, FC is usually measured a bit low. maybe any other WG fans can chime in, i'll message their support as well.

but anyway, those are my numbers. i didn't get to test the fill water yet, i have to run out for a bit and this took me longer than i thought it would already...

 

[mgtfp]

That doesn't look too bad, well done. FC maybe a tad higher as a target for CYA=60.

[EDIT] Forgot that you have a SWG, only after I checked the CSI that I remembered that. So, FC is not too low for SWG at that CYA. But you could raise the CYA a bit. [end EDIT]

How do you calculate the CSI, that value doesn't make sense to me, should me more like -0.1 or -0.14 at 90F water temperature, depending on your salt level. Are you using PoolMath? Maybe you added an extra 0 for the salt level? The pH is actually not bad where it is. With this CH-level, you want to be in the lower 7-range.

For the CH measurement: It is important to swirl thoroughly after each drop. It's a bit tricky to drop and swirl at the same time. You have to add drops until the colour doesn't change anymore. Sometimes you think it has turned blue, but another drop will still change the shade of blue. If it's turned blue, add another drop. If that last drop still changes the shade of blue, then add another one. Once the blue doesn't change anymore, you have reached the endpoint, and you don't count that last drop, that didn't cause further colour changes. The whole sample needs to have changed colour, that's where good swirling is important. Sometimes it starts changing around the drop, but once the drop has been diluted into the sample, the colour changes back.

Especially the TA and CH tests are a lot easier with the speedstir (magnetic stirrer). You get instant mixing and quick and homogeneous colour changes. Especially with higher test levels, I also had the issue that I kept forgetting my drop count while I was concentrating on swirling and colour watching. With the speedstir, I can focus on counting.

 

[crackers8199]

That doesn't look too bad, well done. FC maybe a tad higher as a target for CYA=60.

How do you calculate the CSI, that value doesn't make sense to me, should me more like -0.1 or -0.14 at 90F water temperature, depending on your salt level. Are you using PoolMath? Maybe you added an extra 0 for the salt level? The pH is actually not bad where it is. With this CH-level, you want to be in the lower 7-range.

i didn't calculate it, pool logger did. i didn't do the salt test yet, as i ordered a salt kit with the TF100 but it was out of stock. that actually reminds me i need to e-mail them and find out when it'll be in stock.

is it possible they calculated it with a 0 for salt since i didn't do that test (or input a value for it)?

For the CH measurement: It is important to swirl thoroughly after each drop. It's a bit tricky to drop and swirl at the same time. You have to add drops until the colour doesn't change anymore. Sometimes you think it has turned blue, but another drop will still change the shade of blue. If it's turned blue, add another drop. If that last drop still changes the shade of blue, then add another one. Once the blue doesn't change anymore, you have reached the endpoint, and you don't count that last drop, that didn't cause further colour changes. The whole sample needs to have changed colour, that's where good swirling is important. Sometimes it starts changing around the drop, but once the drop has been diluted into the sample, the colour changes back.

ok, i'm correct at 49 drops (and 1225 calculated value) then. i thought i was done at 49 but added one more to get to 50...but that didn't change the color so i stuck with 49.

is there anything i should be worried about with that high of a CH number? just make sure to keep the pH below 7.5 as often as possible?

Especially the TA and CH tests are a lot easier with the speedstir (magnetic stirrer). You get instant mixing and quick and homogeneous colour changes. Especially with higher test levels, I also had the issue that I kept forgetting my drop count while I was concentrating on swirling and colour watching. With the speedstir, I can focus on counting.

same problem with the speedstir as i had with the salt...it was out of stock when i ordered. i plan to grab one when they're back in stock.

 

[mgtfp]

Yes, I read in other threads that the speedstirs seem to be hard to get these days. Salt is not overly critical, as long as your SWG is happy, but certainly worth checking from time to time. Also has some influence on CSI, so you probably want a good base line since you'll need careful CSI management with your CH level.

I'd recommend to use PoolMath for the CSI calculation, that pool logger value looks wrong. You needed beyond ocean style salt levels to get down to -0.92. Or you did a typo somewhere, probably when entering the pH. If you don't like the PoolMath app, you can also use the old website version:

PoolMath

Discover the calculator behind the perfect pool, PoolMath. Dealing with pools has allowed TFP to become the original authors of the best calculator on the net.

www.troublefreepool.com

I just edited my previous comment regarding FC, forgot that you have a SWG.

 

[crackers8199]

pH up to 7.5 today. Should I be aiming to keep it under 7.5 (and add acid as soon as it goes above that) or let it drift up to 7.8 or higher before adding acid?