Yet another "how do I keep my pH from going up"

[Yoav]

Ah - now's my turn to try and spout nonsense -

If I remember correctly, the process of neutralizing organics with chlorine raises pH. If that is the case, consider the following scenario:
1. Morning - FC drops to 0
2. Possible bathers and other organic stuff enters the water
3. Algae and bacteria thrive without an inhibitor in place
4. Evening - Chlorine dose kills all bacteria and algae, but by now there is plenty of it to kill off, hence a higher pH increase than if their population had been kept in check.

Even if this scenario can somehow effect such a sharp pH rise, I have no way of confirming or calculating it...

 

[Taz]

At the risk of a newbie spouting nonsense, but would installing an ozone generator for such a small pool (and a high turnover-rate) help? I understand there is no residual impact but with Yoav's strong feelings on chemicals ....

(edit) Not that this deals with rising PH.

Cheers - Taz

Hey Taz, what would the Ozone generator help with?

My thought was that it appears you want to minimize FC (you seemed to be targeting 0 FC) while your kids are in the pool, perhaps the oxidizing effect of the O3 would at least provide some benefit whilst they are in the pool. Also, your small pool volume & high water turnover resemble a spa setup where O3 systems may have more impact than on a typical residential pool.

 

[Yoav]

My thought was that it appears you want to minimize FC (you seemed to be targeting 0 FC) while your kids are in the pool, perhaps the oxidizing effect of the O3 would at least provide some benefit whilst they are in the pool. Also, your small pool volume & high water turnover resemble a spa setup where O3 systems may have more impact than on a typical residential pool.

I actually know very little about Ozone sanitation systems. I will look into it, but I have a hunch it is a costly system which is not very common in Israel... I wonder if they even sell it here...
Besides, I have given in to CYA - but thats in my next post...

 

[Yoav]

Well, it seems I have given in to CYA. Again.

This whole business of 0 FC has got me worried to a point where I told my wife that the pool is off limits until I decide how to handle this.
I should have known that that would be the last straw. The season will be over soon, and my wife wants to use the pool (for the kids) - chlorine or no chlorine.

So in went 2 Trichlor pucks tonight.
Since I don't have a reliable CYA test, I would be glad if someone would go over my calculations as I must know exactly how much I am putting in. My target is 20 to begin with and will take it to 30 from there if all goes well.

According to Wikipedia, Trichlor's density is 2.2 gr/cc. My puck measurements are d=8 cm, h=2.5 cm, which equals 125 cc, which means each puck should weigh about 275 gr.
According to the pool calculator, 275 gr of Trichlor adds 10 ppm of CYA (how convenient!).

1. Is that correct?
2. Does Trichlor "get spoiled"? The pucks are in a plastic bucket in the back yard where it is sunny and hot, but it is shaded for the most part. Is there any reason to believe I should pull them out and get new ones instead?

* I am using Trichlor to raise the CYA since I already have the pucks, and CYA powder comes in large bags which cost quite a bit - I don't need that much. That and the fact that they will counter the constant rise in pH to some extent at least.

 

[chem geek]

If I remember correctly, the process of neutralizing organics with chlorine raises pH. If that is the case, consider the following scenario:
1. Morning - FC drops to 0
2. Possible bathers and other organic stuff enters the water
3. Algae and bacteria thrive without an inhibitor in place
4. Evening - Chlorine dose kills all bacteria and algae, but by now there is plenty of it to kill off, hence a higher pH increase than if their population had been kept in check.

You've got that backwards. As chlorine gets used up, such as getting broken down from sunlight or oxidizing ammonia or organics, this is an acidic process so would normally lower the pH. However, at the low levels of chlorine you are using this isn't a big effect and instead you are seeing the rise in pH from carbon dioxide outgassing instead. Also, in the evening you added chlorine which would raise the pH (5 ppm FC with 40 ppm TA would raise the pH from 7.5 to around 7.75) and then the chlorine would react with what is in the water which will eventually lower it pretty much back to where it started -- that is, the net result of chlorine addition and consumption is close to pH neutral (except for the small amount of excess lye in bleach and chlorinating liquid). So again, the pH rise is due to the people in the water moving it around resulting in outgassing of carbon dioxide which raises the pH. As noted earlier, I really don't think your TA is actually 40 ppm -- I think there's a test error there.

I don't think there is enough bacteria or algae to create a chlorine demand unless the FC went to 0 sometime the previous day or night. It's the ammonia and urea (and some amino acids) in sweat and urine that create the real chlorine demand. Specifically, such demand in 15,000 liters is approximately 0.3 ppm FC for every person-hour of being in the pool. Of course, if you aren't adding enough chlorine, then the FC can get to 0 not too long after you add chlorine and that of course would give a much more continuous period of time for bacteria and algae to grow. Are you adding enough chlorine after the swim to ensure that you still get a measurable FC the next morning? If not, then you could have a rather unsafe environment since the chlorine you add after swimming may just be combining with sweat and urine and not having any leftover to kill bacteria or prevent algae.

1. Is that correct?
2. Does Trichlor "get spoiled"? The pucks are in a plastic bucket in the back yard where it is sunny and hot, but it is shaded for the most part. Is there any reason to believe I should pull them out and get new ones instead?

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. If you wanted to get CYA up faster, then you could use Dichlor instead since for every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. Or you could use pure CYA, but that takes longer to dissolve. Though I understand your reasoning since the pucks are low in pH. The problem is that they are slow to dissolve. If you wanted more consistent chlorine levels, then the pucks would be good, but if you eventually go back to your "swim with zero chlorine" approach then using quickly added chlorine would be better -- more like the Dichlor-then-bleach method used for spas where Dichlor is used initially until the CYA level gets to where you want it and then you switch to using bleach instead.

I suspect that your pucks are close to the standard 3" pucks that way 8 ounces or 227 grams so you could use that in The Pool Calculator where one puck would raise the FC by 14 and the CYA by 8.4 though this will take days since the pucks dissolve slowly. The Trichlor density you are using is for solid Trichlor, but the pucks are actually compressed powder so not quite that dense. You should weigh your pucks if you can -- that's the best way to get the right measurement. Trichlor does not spoil unless they get wet so yours should be OK.

 

[Yoav]

You've got that backwards. As chlorine gets used up, such as getting broken down from sunlight or oxidizing ammonia or organics, this is an acidic process so would normally lower the pH. However, at the low levels of chlorine you are using this isn't a big effect and instead you are seeing the rise in pH from carbon dioxide outgassing instead. Also, in the evening you added chlorine which would raise the pH (5 ppm FC with 40 ppm TA would raise the pH from 7.5 to around 7.75) and then the chlorine would react with what is in the water which will eventually lower it pretty much back to where it started -- that is, the net result of chlorine addition and consumption is close to pH neutral (except for the small amount of excess lye in bleach and chlorinating liquid).

Thanks for straightening this out for me. That is an important piece of information I was not aware of.

So again, the pH rise is due to the people in the water moving it around resulting in outgassing of carbon dioxide which raises the pH. As noted earlier, I really don't think your TA is actually 40 ppm -- I think there's a test error there.

So, this means that the two factors involved in actually raising the pH (as opposed to the temporary effect of FC before it is consumed) are CO2 outgassing and lye. I just measured the pH and FC (morning time). Seems FC hasn't changed much during the night. pH though has risen to 7.1 (about 0.2 difference from last night's reading before adding chlorine). Granted, there have been two pucks in a floater for about 4 hours in there, but I don't think they would have any significant effect on pH in such short a time. Either my chlorine has lots of lye in it, or teapot was right about my moving water having a significant effect on outgassing (or of course both)

I don't think there is enough bacteria or algae to create a chlorine demand unless the FC went to 0 sometime the previous day or night. It's the ammonia and urea (and some amino acids) in sweat and urine that create the real chlorine demand. Specifically, such demand in 15,000 liters is approximately 0.3 ppm FC for every person-hour of being in the pool. Of course, if you aren't adding enough chlorine, then the FC can get to 0 not too long after you add chlorine and that of course would give a much more continuous period of time for bacteria and algae to grow. Are you adding enough chlorine after the swim to ensure that you still get a measurable FC the next morning? If not, then you could have a rather unsafe environment since the chlorine you add after swimming may just be combining with sweat and urine and not having any leftover to kill bacteria or prevent algae.

That does not seem like the case. I add 2 ppm FC in the evening and most of it is there the next morning only to be broken down by sunlight. I do get the occasional boatman insects in the water despite the chlorine. I think they only disappeared once about a week ago when I put in about 10 ppm FC. I don't think their presence is an indication of a problem... is it?

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. If you wanted to get CYA up faster, then you could use Dichlor instead since for every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. Or you could use pure CYA, but that takes longer to dissolve. Though I understand your reasoning since the pucks are low in pH. The problem is that they are slow to dissolve. If you wanted more consistent chlorine levels, then the pucks would be good, but if you eventually go back to your "swim with zero chlorine" approach then using quickly added chlorine would be better -- more like the Dichlor-then-bleach method used for spas where Dichlor is used initially until the CYA level gets to where you want it and then you switch to using bleach instead.

I am not sure I understand what you meant. Going for the CYA is a farewell to the swim in 0 FC approach. I am attempting to reach the lowest CYA level that will allow me to keep a reasonable amount of FC during daytime until I can raise it back at night, with your recommended 30 ppm as the ceiling. I am only using the pucks as a cheap (and readily available) source of CYA, after which I go back to bleach. It will just take some time to get there. I'd rather take this one slowly than be sorry.

I suspect that your pucks are close to the standard 3" pucks that way 8 ounces or 227 grams so you could use that in The Pool Calculator where one puck would raise the FC by 14 and the CYA by 8.4 though this will take days since the pucks dissolve slowly. The Trichlor density you are using is for solid Trichlor, but the pucks are actually compressed powder so not quite that dense. You should weigh your pucks if you can -- that's the best way to get the right measurement. Trichlor does not spoil unless they get wet so yours should be OK.

I will have to weigh them then. At least I am safe from overshooting my CYA target

 

[teapot]

Hi Yoav,
From what I can see,originally you wanted to run with low chlorine levels and you have just added 2 regular tabs of chlorine to 15,000 litres of water? that will certainly sterilse the water and give you a considerable chlorine hit. 1 would have been plenty.

Not sure about the use of a Variac (that's an old word) to vary the speed of your pump, the usual way I believe is via an motor inverter with phase adjustment. This are available as DIN rail additions for the power/fuse unit.

 

[Yoav]

Hi teapot.

My intension of running with low chlorine would have been facilitated by having no CYA in the pool. But after reconsidering the downsides we've discussed in this thread (and with a slight push from my wife), I've decided to give it up and use CYA - which would mean normal treatment levels for the target amount of CYA; in my case the target is 20-30 so I will be targeting 2-5 ppm of FC.

My use of Trichlor tablets is not for the FC at all - which is a nice byproduct BTW until I reach my target CYA - its for raising my CYA (which is why I'm using two at a time).

As for chlorine levels, the range of FC in the pool with two tablets in, ranges from about almost none during daytime to about 1.2-1.5 at night.... So its not much generally speaking (its a lot as long as my CYA levels remain low though)

(I am not sure as to the reactivity of the FC coming from Trichlor tablets, that is to say I don't know if the FC coming from the tablets is reactive in proportion to the CYA in the pool or in some other fashion if it is somehow initially bound to the CYA)

As for the Variac / Autotransformer - thats the only method I know of to control AC voltages efficiently without having to buy expensive power conversion units such as switching power supplies and inverters.

I will check about the inverter option. When you say phase shift, do you mean that is the method of adjusting power, or are you referring to PFC which would be required for an inductive load such as a motor?

Yoav.

 

[chem geek]

(I am not sure as to the reactivity of the FC coming from Trichlor tablets, that is to say I don't know if the FC coming from the tablets is reactive in proportion to the CYA in the pool or in some other fashion if it is somehow initially bound to the CYA)

The binding and releasing of chlorine to/from CYA happens very quickly, effectively in less than a second independent of the source of chlorine. So the amount of active chlorine in your pool will be a function of the FC level and the CYA level in the bulk pool water no matter what source of chlorine you are using. So initially with lower CYA, the active chlorine level is higher and this will drop as the CYA rises. So once your CYA is where you want it, you switch to another source of chlorine that won't add CYA.

 

[Yoav]

Thanks Richard.
This means that until my CYA rises, there are very high levels of active chlorine in the pool. Maybe I should throttle it down a bit.

One more added bonus of using the tablets (until I switch back to bleach) is the acidity. I expect my quickly-rising pH will either slow down or stop rising altogether for the duration.

 

[chem geek]

This means that until my CYA rises, there are very high levels of active chlorine in the pool. Maybe I should throttle it down a bit.

I wouldn't say very high, though higher than normal. The lowering of active chlorine concentration even with a small amount of CYA. Let's say that 3 ppm FC is what is being maintained, then initially when the CYA is 1.8 ppm (from Trichlor releasing cumulatively 3 ppm FC), the active chlorine is the same as in a pool with 1.9 ppm FC with no CYA. After say another day with another 3 ppm FC replenishing that lost, the CYA is now 3.7 ppm and the active chlorine equivalent to 1.1 ppm FC with no CYA. Then this becomes 5.5 ppm CYA with an active chlorine equivalent to 0.7 ppm with no CYA.

These levels aren't much higher than found in indoor pools that don't use CYA. It's higher than one could have if CYA were present. If you were at 30 ppm CYA then with around 3 ppm FC this is roughly equivalent to 0.1 ppm FC with no CYA so you can see how this is much lower than that above.

In spas, one typically uses Dichlor powder to raise the CYA since 1) it dissolves quickly and 2) it gives more CYA with the chlorine (for every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm) so the higher active chlorine exposure is for a shorter period of time. The use of Dichlor is net acidic, though not as much as when using Trichlor.

Anyway, you can lower your target FC while the CYA is building up, at least for the first few days, if you want to.

And yes, the Trichlor acidity compensates for the pH rise in your pool and will slowly lower the TA over time, at least as long as the Trichlor is used (but at some point the CYA will be at your target and you'll stop using the Trichlor).

As waterbear (a former member of this forum) used to say, "it's a pool, not a chemistry experiment!" so don't overthink this. For your purposes (next time you refill since you've already started out with Trichlor this time), I'd just use the Dichlor-then-bleach method similar to spas since that should accomplish your goals of a low FC when you enter the pool and minimal chlorine effects during use of the pool. Though it's technically not as strongly protected as commercial/public pools, the risk is very low so long as you add sufficient chlorine after pool use to carry you over to the time you use the pool.

 

[Yoav]

Absolutely amazing!

Richard, I don't see how it could happen so soon, especially with so little CYA in the water.
It seems those active FC numbers you gave in your previous post - that "1/x 'ish" active FC to CYA ratio - has reared its ugly head already.
Its been only three days of 2 Trichlor pucks instead of bleach and lo and behold - algae has started growing on select surfaces.

The paradox -
I need the CYA to keep chlorine (even in small amounts) in the pool during daytime in order to prevent fast-growing bacteria, which comes at the expense of the kill-potential of the chlorine - that which the slow growing algae need a lot of apparently.

I will re-start the 2 ppm of bleach every evening routine in addition to the pucks in hopes that it will hold back the algae.

On a happier note, my pH has remained ~7.2 for over two days now. Whatever you say about those 'gawdawful' tablets, they are apparently very well suited for my local pH environment.
Will have to get me an acid feeder (as Jason recommended it to someone else with high fill water TA) once I go back to bleach.

 

[teapot]

Yes it's a paradox for a while, Yoav, you need to shock dose your pool and hold the free chlorine at a higher level than 2ppm in order to kill off the algae and oxidise it otherwise you are just slowing the growth down until your available chlorine is used up at which point the alage just re appear. Shock is not a one off addition it is a time consuming and chlorine consuming process. You ideally need to raise the chlorine to 5ppm and hold it there until you have sanitised the water properly at which point you can reduce the chlorine to the regular amount.