Bleach affects pH?

[brucek2]

Is it possible that bleach can push pH up? I've read the pool school materials and used the calculator, and don't see any indications that it should, but I can't think of why else my pool suddenly has much higher pH

Measurements (yesterday -> today)
FCL 0.5 -> 4.0
CC 0 -> 0
PH 7.5 -> 7.9
TA 60 -> 60
CH 150 -> (not measured) (will add more hardness soon)
CYA (last measured at 24 a few days ago, then added 64oz CYA powder)

The only chemical I added between the two readings was about 48oz of WalMart Great Value brand 8% bleach. Well that plus the CYA from a few days ago is probably still dissolving but I'd expect that to push ph down not up?

So my questions are:
1) could this be from bleach?
2) if so will it also fall again as the fcl is consumed?
3) if #2 is true is the idea that I'd start to think about the fcl ranges I want to be in, and how much bleach that means I'll be adding, and therefore how much MA I have to add so that even with the rise I'm still at acceptable ph?

Thanks!

 

[linen]

Using bleach is basically ph neutral process.

Basically get your FC to it's target level. If the FC level is below 10 ppm, then you can adjust ph.

Are you getting any aeration? Fountains, lots of splashing, return breaking the water, etc.?

 

[jblizzle]

The bleach is pH neutral when you consider the FC level you start at ... meaning that yes adding bleach may raise the pH slightly, but as the FC is consumed back to where you started the pH should come back down to where it started.

This is one reason we always say to adjust the pH to the lower 7s before starting the shock process as adding all the bleach will raise the pH (but once the FC > 10ppm, you can not test and adjust the pH).

 

[brucek2]

So it sounds that just like FCL is expected to fall and rise from consumption/addition, so to is pH as part of that same process? That makes sense, just means I need to be comfortable with both the low and high points of the pH cycle. I'm still just learning/getting started, that's all probably doable as I get comfortable with my pool's routine.

I'm not attempting a shock, just trying to figure out how to get to my pool's operating range. I was low yesterday and tried to correct for that by adding a lot of bleach in one day. Once I'm there I think most days I'd need to add just a fraction of that, so the rise/fall will be milder.

There may be some mild aeration from water going over the infinity edge (which is mostly a trickle straight along the wall with not much of a splash), but that's been a constant through several days of a flat pH of 7.4-7.5. I don't think its adding much on its own.

 

[linen]

It is a small change regardless. Lets say you start at 8 ppm FC, when you redose the next day back up to 8 ppm FC, you net ph change due to the chlorine addition is 0. One caveat to this is sometimes cheap bleach (or some higher concentrations of LC) have more lye in them and do cause a slight rise in ph. I would guess your walmart bleach is not one of the ones with excessive lye though.

 

[brucek2]

There's something else going on here. Out of curiosity I stopped replenishing the chlorine and by this afternoon it had fallen all the way back to 0.5. But the pH did not drop back with it -- it is still 7.9.-8.0. I've also still seen no downward pressure on the pH from the CYA I added six days ago (which per the pool calculator should have brought pH down 0.5.)

Some possible theories:
1. The pool calculator has a typo/bug re: adding stabilizer. It says that pH will be lowered but actually it will be raised (in which case my pool is tracking near perfectly?)
2. The WalMart Great Value brand 8% bleach has the excessive lye issue. Is it possibly exacerbated by adding a lot at once vs. gradually over time? If so I better not add any more or get used to adding MA along with it every time.
3. The calcium hardness product I added a week ago had an extra ingredient that raises pH. While the store clerk swore it was just calcium chloride, there's a decent chance she was just telling me what I wanted to hear. But even so there's the issue that pH did not move at all for the first couple days after adding this product -- would it have a strong delayed effect?
4. Something else?

 

[jblizzle]

1. Nope
2. Not likely, never observed that myself.
3. Maybe, doubtful.
4. ?

You have any aeration?

 

[chem geek]

Adding bleach to go from 0.5 ppm to 4 ppm FC in 17,000 gallons with the TA of 60 ppm and CYA of 24 ppm would have the pH rise from 7.5 to 7.75. Adding 64 ounces of Cyanuric Acid (CYA) should have the pH drop to 7.12, but CYA can take days to dissolve (it's faster if in a sock over a return).

So it's not just the bleach, but the acidity of CYA you aren't seeing either. So you've got something going on in your pool having the pH rise pretty quickly and since your TA is fairly low that's strange. Your pool didn't get recently re-plastered, did it? Your pH, TA and CH are low for a plaster pool (at pH 7.5 your CSI is around -0.5) -- are you finding that your CH is rising or is not dropping as expected with water dilution (depending on the CH of your fill water)? If you notice this sort of change in CH along with pH rise, that's an indication of calcium carbonate dissolving from your plaster. Do you notice the surface getting pitted (tiny holes)?

 

[brucek2]

This morning's measurements:
FCL 1.4 CCL 0
pH 8.0+
TA 60 (turned clear) - 70 (turned blue)
CH 160
CYA 30

Seems pH is still rising. CH may be slightly up or may be within my measuring error. I don't see any pitting but its possible I just don't know enough of what to look for. Pool was plastered 15 years ago. It's been a week now since I added the CYA (in two socks in the skimmer basket), the granules are long gone but not much of an effect. I wonder if it maybe went bad / lost strength while sitting on the retailer's shelves for months?

I like the guess about the plaster since we know CSI is low, although its curious that even while low CSI was a constant, the pool pH stayed at 7.5 for days then spiked overnight. Same concern about aeration -- there probably is a mild amount from water trickling over the infinity edge (it doesn't really splash), but that happens every day too. Now I did run the pumps for 48 hours straight (vs normally 4 hours/day) after adding the hardness product a week ago, and it was a couple days after that the pH spiked, so maybe it was enough to push it up?

Anyway my hardness product came in yesterday, so I'm thinking today I'll start with about half of that 25lb container, along with a couple cups MA to hopefully bring down the pH and since I still have some leftover trichlor pucks I'll throw a couple of those into the feeder to add some CYA.

 

[chem geek]

An infinity edge if continually spilling over is a LOT of aeration.

 

[easttn]

I have to add acid to mine about every 3 or 4 days. I figured it was the bleach raising it too. I also use the great value bleach. I dont have any aeration. TA 120, CH 200. I thought the pH of bleach was 12.

I have to add about 5 cups of pH 12 bleach per day and about every third day I have to add 1.5 cups of pH 1 sodium bisulfate to get my pH back where I started. That would equal 15 cups of ph 12 to 1.5 cups of pH 1. That would make is sound like I needed 15 cups of acid to equal out the 15 cups of bleach I put in. Looking at it like that then Im getting away cheap by using that small amount of acid. Not sure if that equation is the right way to look at it but I threw it out there.

 

[chem geek]

The higher pH of bleach means that it raises the pH upon addition. No one is disputing that. However, when bleach breaks down from sunlight or oxidizes ammonia or nitrogenous organics, this is an acidic process and the pH drops back down (technical details in this post). We've got lots of pools with fairly stable pH using bleach or chlorinating liquid. Your TA of 120 ppm is on the high side and you may find less of a pH rise if you lower it substantially to no higher than 80 ppm. TA is a measure of how much the water is over-carbonated and carbon dioxide outgassing makes the pH rise (this chart shows how much a pool is over-carbonated at various pH and TA). Also note that you don't want to lower the pH below around 7.5 and if it wants to settle in at 7.7 or 7.8 that's OK.

I have to add about 5 cups of pH 12 bleach per day and about every third day I have to add 1.5 cups of pH 1 sodium bisulfate to get my pH back where I started. That would equal 15 cups of ph 12 to 1.5 cups of pH 1. That would make is sound like I needed 15 cups of acid to equal out the 15 cups of bleach I put in. Looking at it like that then Im getting away cheap by using that small amount of acid. Not sure if that equation is the right way to look at it but I threw it out there.

pH is a logarithmic scale and you need to account for pH buffering/capacity so your calculations are not correct. If the chlorine were not used/consumed with an acidic process, then the 5 cups of 8.25% bleach would require 4 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) or 5.4 ounces weight (3.6 ounces volume) of dry acid to compensate for pH so over 3 days that's 2 cups. Though you are using somewhat less than that, most of it is because of carbon dioxide outgassing from your higher TA. Aeration from waterfalls, spillovers, fountains, splashing, etc. increases the rate of that outgassing and therefore the rate of pH rise.

Some bleach is higher in pH due to excess lye (some are closer to 12.5 or more), but Clorox tends to be at around 11.9 and is low in excess lye.

In my own pool, I add about 2 cups of 12.5% chlorinating liquid (pH probably around 12.5) every day, so if there were no chlorine usage/consumption that was acidic, I'd have to add 2.4 fluid ounces of full-strength Muriatic Acid every day or about 2 cups every week. I add much less than that (about 1/4th to 1/3rd that amount).

If you had an algaecide in your pool such as Polyquat 60, you could let the FC drop to zero and then see that the pH of your pool water still rises as long as you keep adding acid to keep the pH lower. That's a risky experiment as you could still get algae, but it would demonstrate the point.

 

[easttn]

Nice piece of info. Thanks. What are the red, yellow and green numbers trying to tell me in the co2 chart?

I wasnt really worried about the amount of dry acid I was using, just giving an example that I was in the same boat as him. I figure whether I add acid now to lower the TA or a number of times through the season, its going to cost me the same amount of acid. Unless I'm missing something.

I think I will take your word on the pH rise, instead of trying to play with the big green algae monster.

 

[JamesW]

This morning's measurements:
TA 60 (turned clear) - 70 (turned blue)

The TA test turns red, not blue. Are you sure that you're doing the test correctly?

Have you recently heated the pool? Warmer water holds less CO2.

Does your solar introduce aeration into the return lines?

What is your current water temperature?

 

[brucek2]

Oops, my mistake when I wrote the post, I confused the CH test colors with the TA test. Good catch.

I have recently started using the solar system to heat the water from 80 (day time temp, very consistent) to 85. I mix the water from the panels (120?) with a bypass line of unheated water so the return stream is about 90. Night time air temp gets down to 70 or so, not sure how far the water goes with it. I've never seen air in the streams from the return lines.

pH is finally moving down. It was 7.8 this afternoon, I think due to the 2 cups of MA I put in yesterday. I'll keep an eye on it, starting to lean towards the theory that the two days I kept the pumps running full time are the most responsible for the sudden spike and that there may be more subtle ongoing upward pressure from even the 4 hour / day aeration.

CH is up to 250 now, if I reach a point where there's no rising pH at all maybe that'll mean it wasn't the aeration and it was period with low CH?

 

[JamesW]

Your signature shows a CL-220 tab feeder, have you been using tabs, or just bleach?

Have you been adding fill water recently? Perhaps to make up for extra evaporation? How much?

What are the readings from your fill water?

 

[brucek2]

My pool service quit a few weeks back. That's when I discovered this site and learned what CYA was and that my currently level of 240 was probably not great.

So I started by replacing about 90% of the water. The pool service had been putting tabs in the feeder, but my plan was to go just with bleach during a transition period and then soon with SWCG. I've got a couple tabs in there now though just to help bring CYA up (last measured at 30, I'd like to get to 70 or so.)(I should add I don't think any were in there at the time of the pH spike.)

I have not added water myself since the refill, although there's been some rain. There's also an auto-fill valve on the trough outside the infinity edge. The water level in the main pool is always right up to that edge so I don't see many clues either way as to how much water is lost or added. I haven't seen dilution in TA, CH, CYA though so I'm guessing that fill water influence so far has been small?

 

[chem geek]

What are the red, yellow and green numbers trying to tell me in the co2 chart?

The color coding is just ranges from <10, 10-20, >20, but the point where pH rise is noticeable is dependent on the amount of aeration of the pool water so just look at the numbers in a relative sense. The bottom line is that you lower the TA level if your pH tends to rise over time.

 

[easttn]

The color coding is just ranges from <10, 10-20, >20, but the point where pH rise is noticeable is dependent on the amount of aeration of the pool water so just look at the numbers in a relative sense. The bottom line is that you lower the TA level if your pH tends to rise over time.

Yes I understand the TA level and pH rise that comes from it, but its nice to look at a chart like that and see what to expect if something changes. Would this chart be at sea level? If so what would one expect at 1000, 2000, 3000 feet above sea level?

Why dont you put this kind of stuff in the Pool School? I think there are people who would like to improve on their knowledge of this kind of stuff.

 

[chem geek]

I figure whether I add acid now to lower the TA or a number of times through the season, its going to cost me the same amount of acid. Unless I'm missing something.

You are right that the lowering of TA procedure is a "pay me now or pay me later" sort of tradeoff since 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) per 10,000 gallons will lower the TA by 10 ppm regardless of whether this is done all at once during the lowering TA procedure or whether it is done over a longer period of time. Of course, over a longer period of time other things can change the TA including evaporation/refill which can increase TA and water replacement which can either increase or decrease TA depending on the TA level of the fill water relative to the pool.

Would this chart be at sea level? If so what would one expect at 1000, 2000, 3000 feet above sea level?

Why dont you put this kind of stuff in the Pool School? I think there are people who would like to improve on their knowledge of this kind of stuff.

The CO₂ chart is too complicated and not as meaningful as just saying what is already in the Pool School which is the following regarding TA:

Total alkalinity indicates the water's ability to buffer PH changes. Buffering means you need to use a larger quantity of a chemical to change the PH. At low TA levels, the PH tends to swing around wildly. At high TA levels, the PH tends to drift up.

There are many factors influencing the rate of pH rise including aeration (including circulation) and temperature and yes, altitude. However, even at 5000 feet, air pressure is only around 15% lower than sea level so the numbers in the chart don't change that much. Again, they are only useful as a relative guide and the actual rate of carbon dioxide outgassing tends to vary with the square of the TA, not what is shown in the chart which is the degree of over-carbonation of the water.

We do use the relative principles of what the chart implies when describing how to Lower Total Alkalinity which is another Pool School article. The procedure has one lower the pH and aerate the water because as you can see from the chart a lower pH is more over-carbonated so results in faster carbon dioxide outgassing. Aeration also speeds up the process (though that is not shown in the chart).

These sorts of technical details are on this site -- just not in the Pool School. The Deep End has a large variety of in-depth topics including Pool Water Chemistry, Certified Pool Operator (CPO) training -- What is not taught, Degradation of Cyanuric Acid, pH Buffer Capacity, Water Absorption and Heating from Sunlight, Solar Panel Technology Comparisons, and many more, plus other detailed articles in other topic sections, usually as stickies, such as Hydraulics 101 - Have you lost your head? that is a sticky in the Pumping Station topic area and there are many other stickies as well.