PH Questions

[Charlie]

Hi everyone,
I have 2 questions regarding PH readings:

1. Do they make a test kit, or strips, that can read higher than 8?

2. Is it better to put acid in when the water is circulating or still?

Reason for question #1 is I have a salt water pool, and I have to adjust my ph all the time. My Taylor kit only goes to 8, and I thought when it was indicating 8 I added about 1/4 of a gallon of acid and the next day it was still reading 8. So I added more until I got it down to 7.6.

Reason for question #2 is when I bought acid, the person behind the counter said would work better adding it in the deep end without the water circulating. I asked why, and he said you use less acid and it won't impact your Alkalinity.

[chem geek]

I don't know about #1 -- the Taylor K-1000 pH test (and I believe Ben's kit) will read to 8.2 while the Taylor K-2006 kit will read to 8.0, but I'm not aware of kits that read higher.

#2 is pure bunk. The "acid column" or "slug" method was debunked here (http://jspsi.poolhelp.com/JSPSI_V1N2_16-30_AcidColumn.pdf). Basically, no matter how you add acid, the TA will be lowered. 25.6 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons will lower the TA by 10 ppm no matter how it is added. The only difference is that depending on the amount of aeration, the pH may not drop as much because aerating the water has the pH rise with no change in TA. Be very careful because dumping the acid in one place without circulating can be damaging to pool surfaces since the pH will be very, very low and will tend to pool near the bottom if it doesn't mix so this should never be done (and it's not effective anyway so why bother).

You should read Water Balance for SWGs (http://www.troublefreepool.com/pool-school/water_balance_saltwater_generator) where you can learn how to slow down the rate of pH rise. Lowering your TA should help (this was first figured out in this thread (http://www.poolforum.com/pf2/showthread.php?t=5379)). The use of 50 ppm Borates can also help (this was first figured out in this thread (http://www.poolforum.com/pf2/showthread.php?t=4712)). Having the CYA level higher at 70-80 ppm can also help if your pool is exposed to a lot of sunlight (but you need to maintain a minimum FC of 4 ppm in this case).

Richard

[CarlD]

Charlie,

Richard doesn't intend to be harsh on you but rather is upset with our on-going battle with pool store clerks who continually distribute mis-leading, false and even dangerous information.

Everything the clerk told you is totally wrong, which you would not have known--that's why you asked the question.

If you add acid to a pool without the filter running, you risk damaging it, if that "slug" of acid reaches the sides or bottom. This is particularly dangerous for vinyl pools as it can soften and weaken the vinyl where the water pressure is highest. You should ALWAYS add acid with the filter running and you should dilute it first. I like to pour it into a 5-gallon bucket of water first. Then it is far less likely to damage the pool (who cares if the wall of the bucket is etched, right?).

Pool stores have been teaching the "slug" method for lowering Total Alkalinity for years--it doesn't work. Funny, the clerk said it would NOT lower your alkalinity--he's right for the wrong reason and wrong for the right reason.

See, T/A AS MEASURED goes up as pH rises and down as it falls. You can raise T/A additionally by adding baking soda or washing soda (sold expensively as "Soda Ash" or "pH Up!" in pool stores, and cheaply as Arm&Hammer Washing Soda).

To lower T/A, you use the "trick" of lowering it by lowering the pH. But now you have to find a way to RAISE pH without raising T/A as well. The only practical way is by AERATION.

Aeration can be accomplished with a fountain, a gang of 12-year olds, a waterfall, or just leaving the pool uncovered with the returns pointed at the surface.

Since NONE of this is known to pool store clerks, they still recommend the old slug method. This sort of seems to work but only if:
a) pH is lowered sufficiently--but adding the acid with the filter running will do it faster.
b) Aeration happens unintentionally--by leaving the pool uncovered and having a bunch of kids in it.

As for Richard's other comments, they are WELL worth pursuing.
1) pH is known to rise with SWG pools. Lower T/A levels, like around 80-90ppm, should help, but you may still find you have to add more Muriatic Acid than anything else.
2) Borates at the 50ppm level should help stabilize the pool as well.

BTW, if your pH is over 8, you are already in trouble and need to get it into the 7's or the effectiveness of chlorine will be drastically reduced.

[chem geek]

I was told by a member on another forum about two Taylor test kits that have larger ranges: Taylor K-1285-1 (http://www.taylortechnologies.com/products_kitinfo.asp?&MarketID=1&KitID=2209) and Taylor K-1592 (http://www.taylortechnologies.com/products_kitinfo.asp?KitID=2364). However, these really aren't necessary since this problem of being so far out of range is usually quite rare and generally one can just try using amounts of acid or base to move up to 0.5 pH units at a time until one gets into range.

The Pool Calculator (http://www.thepoolcalculator.com/) can be used to calculate dosages, but for moving the pH these calculations are approximate. I have the accurate calculations in the Pool Equations (http://richardfalk.home.comcast.net/~richardfalk/pool/PoolEquations.xls) spreadsheet, but it's not easy to use.

Also, if one has the acid and base demand tests in the Taylor K-2006 or equivalent kit, then that can be used to determine the amounts needed. Generally, these tests aren't that useful because they are too coarse, but when the pH is out of range and larger adjustments are needed, then these tests will work better.

Richard

[Charlie]

Thanks gents for the info. Raising pH will never be a problem in my pools since I have a small waterfall from the spa that dumps into the pool. In fact, pH is the only item that I have to keep an eye on all the time. I do have a SWG pool.
Readings today using a Taylor K-2006 test kit
FC: 3.6
CC: 0
pH: 7.6
TA: 130
CH: 360
CYA: 50
Salt: 3200
Phosphate: < 100
My saturation index is 0.0 Neutral using Perfect Pool & Spa software.
http://www.perfectpoolandspa.com/

I just added 1/2 gallon of acid to reduce the TA more. My pool is ~14,000 gallons plaster.

[chem geek]

Though the aeration from your waterfall and the bubbles from the SWG are contributing to the pH rise, the higher TA of 130 ppm is making things that much worse in terms of the rate of pH rise. Read HOWTO: Lowering Your Alkalinity (http://www.poolforum.com/pf2/showthread.php?t=191) and see if you can get your TA down to 80 ppm. As for the saturation index, the tool you are using is resulting in an index that is slightly too low. The Pool Calculator I linked to earlier has a slightly more accurate index calculation (not a huge deal, however -- you don't have to be precisely at zero).

If you end up at 80 ppm for TA and find that reasonable, then you could somewhat raise the CH level to compensate or you could target 7.7 as your pH. Again, not a huge deal here -- 0.1 or 0.2 (+/-) on the index isn't a problem.

[Charlie]

I was finally able to get my pH down to 7.2 last night when I checked it. It was 6 hours after adding 1/2 gallon, so it went from 7.6 to 7.2 with 1/2 gallon of acid added.
I'm going to check it when I get home from work today, and more than likely, I will be adding acid to keep it at 7.2 (according to those instructions in the link posted by Richard).

How long (estimating) will it take to get the TA down to the 80 range with this method? Just trying to get a ball park number only. Thanks,
Charlie

[CarlD]

It really depends....if pH is rising from aeration, then the more you aerate, the faster it rises, and the faster you can add acid to bring down pH and TA together.

But if the pH is rising from something else and the TA is going up with it, it will take far longer. The thing to do is check TA each time you bring the pH down to 7.2 and you'll see how long it takes.

[Charlie]

Just checked it at 5:30pm my time, and the pH is now 7.4 and the TA is 110. From these numbers, it looks like it will take me ~2 weeks ± a day or to in order to hit my target of 70.

[chem geek]

Try pointing all of your returns upward. You could also be a little more aggressive with the acid getting closer to 7.0 without overshooting (kind of the color between 7.0 and 7.2). It is a slow process, but I don't think it will take quite as long as you think.

[Charlie]

Just an update:
pH: 7.2
TA: 80
CYA: 50 (was 40 yesterday)

I added stabilizer yesterday, but I probably need to let it go for a few more days before I can an accurate number?

Just a little bit more to get to a TA of 70.

[aylad]

If you added it through a sock hung in front of a return, then I would give it at least 2-3 more days before you get the accurate level.

Janet

[Charlie]

Finally got my TA to 70. My pH is currently 7.2. From all this daily testing, it looks like my pH goes up ~0.1-0.2 each day. Just need to bring up my CYA to 80. Its currently at 60.

[chem geek]

The rate of pH rise will likely be faster at the lower pH so see what it does when it gets closer to 7.7. You may want to target a pH a little higher than 7.5 and not try and lower it below 7.5 in the future.

[Charlie]

With my levels getting closer to the recommended amount, I've created a spreadsheet to document the tests. Here is what I have, and let me know if these values are okay or not. I hope I'm close:

I've pasted the values in a Word Document for easier viewing:
http://mysite.verizon.net/res6ncxf/TEST.doc

[chem geek]

Your Minimum column has too low an FC (2) for the CYA level (60). For an SWG pool, it should be an FC of 3 for a CYA of 60. Basically, shoot for an FC that is a minimum of around 5% of the CYA level. This is lower than in Ben's chart used for manually dosed pools, but seems to work well for SWG pools.

You don't need to worry about the phosphate level. I've got 2000-3000 ppb phosphates in my pool and am able to control algae using chlorine alone (well, this year I also have borates in the pool, but I didn't before this year). You might consider using 50 ppm Borates in your pool since this helps to control pH rise, helps prevent scaling in the salt cell, and also inhibits algae growth.

Your minimum numbers are way too low when taken as a whole. The low pH, TA and CH combine to produce a saturation index of around -0.8 which would tend to dissolve the plaster in your pool. The ideal levels you listed have a saturation index of around -0.3 while the maximum levels have a saturation index of around +0.2. You should use The Pool Calculator (http://www.thepoolcalculator.com/) to calculate the saturation index and try to target something close to zero or perhaps slightly below (i.e. -0.1 or -0.2 but not much lower) to lessen scaling in your salt cell.

Generally, to minimize the rate of pH rise you want your TA at around 80 ppm and your CYA at 80 ppm. That means your FC should be 4 ppm minimum and for decent water balance with salt at 3000 ppm your pH target should be around 7.7 and your CH at 300-500. If you target your pH at 7.6, then your CH should be 350-600.

Richard

[Charlie]

Thanks Richard for your review. That makes sense - the saturation index is what I should use to target minimum and maximum levels.

[chem geek]

Roughly speaking, one sets the CYA level according to the amount of sunlight protection they need, though usually not too high (with SWG pools, 80 ppm is OK if the FC is set at 4 ppm or higher). Then with the CYA level, this determines your FC target.

You set your TA appropriately for your source of chlorine. For hypochlorite sources, you set your TA on the low side, usually around 80 ppm but sometimes lower if the pH tends to rise. The pH target is usually around 7.5, but for SWG pools where the pH tends to rise it could be 7.7. After all of these are set, then you add enough calcium to have the CH high enough to have the saturation index close to zero. So in an SWG pool, with its higher salt level and a tendency for the pH to rise, one may have a lower TA and a higher CH than in non-SWG pools.

Richard

[Charlie]

My saturation index is -0.8 with these readings this morning:
Water Temp: 60°F
FC: 5.0
CC: 0
pH: 7.4
CH: 425
CYA: 80
Salt: 3200

I can lower the index by increasing the CH, but what are the disadvantages of increasing the CH? Looks like I need to add a little of Arm & Hammer baking soda but it still will not get me close to -0.1 or zero.

[chem geek]

You didn't list the Total Alkalinity (TA), but with the numbers you did list then the TA would be about 55 ppm to get a saturation index of -0.8. Is your TA really that low? I would raise your TA level to 80 ppm using baking soda (or at least 70 ppm, but see below for more info). This may somewhat raise your pH which would also be fine. After adjusting the TA, if the pH is below 7.7, then you can raise it using some 20 Mule Team Borax (one could raise both pH and TA using pH Up, but that gets tricky to do properly).

Also, do you have 50 ppm Borates in your pool?

The adjustment of TA to 80 and pH to 7.7 would bring the saturation index to -0.25 which is on the low side, but not as bad as -0.8. As for whether it makes sense to raise the CH to 500 or 600 ppm, this depends on what normally happens in the summer when the pool water is warmer and you are using the pool. If a pH of 7.5 were fairly stable, then a higher CH would be appropriate, but if the pH tended to rise and was more stable at 7.7, then keeping the CH where it is and targeting a 7.7 pH would be better.

Normally as the water temperature drops, the pH should rise, all else equal. I'm not sure why, with an SWG and your small waterfall from the spa, your pH is as low as 7.4. Have you been adding acid to keep the pH lower? I'm confused because you used to have a problem with the pH rising so you lowered the TA to 70 and I suggested that you not try and lower the pH below 7.5 and keep a higher pH target. For your TA to have dropped, you must have been adding acid over time. I repeat my advice that you should not try and fight to keep a pH of 7.5 in an SWG pool. If you really, really want to have that pH, then you'll need to not only have a low TA and 50 ppm Borates, but have a much higher CH. Most people just target a pH of 7.7 instead and that works out well.

Richard

[Charlie]

Old age...
TA=60
I did add 2 cups of Arm & Hammer baking soda yesterday. I'm targeting 70-80.

I do not have Borates in the pool. Where or how do I go about getting some?

My pH does rise since I have a small water fall from the spa into the pool. As for targeting 7.5 as the low, yeah I've been trying to figure out how much to add so I have a general idea when its at 7.8 I add "xx" amount in. OK so I'll target a pH of 7.6-7.8 or even 8.

[chem geek]

The addition and use of borates is described in this thread (http://www.poolforum.com/pf2/showthread.php?t=4712). You can use The Pool Calculator (http://www.thepoolcalculator.com/) to calculate dosages of 20 Mule Team Borax and Muriatic Acid, or of boric acid if you get that directly (see this post (http://www.troublefreepool.com/post87988.html#p87988)).

The Borates will make the pH rise slower and might lower the total cumulative acid addition needed over time if you are able to lower your SWG on-time due to the algaecidal properties of the borates. As for pH, I wouldn't go so far as 8.0. I think that after the borates a ph of 7.7 is going to be reasonable stable.

[Charlie]

Thanks Rich for that info. Interesting on how much of 20 Mule Team you need to add, which brings me to this question: since you are adding so much in the pool, what does that do to the DE filter pressure? Will I see a huge increase? My pool is ~14,500 gallons.

[chem geek]

You won't see any change in pressure -- I presume you are adding it directly to the bulk pool water. What you add to water is like adding salt -- it fully dissolves. It does have a small effect on Total Alkalinity -- 50 ppm Borates at a pH of 7.5 increases TA by about 5 ppm -- but you can use The Pool Calculator to calculate the saturation index and it will account for the Borates (assuming you put that into the calculator).