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. 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 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). The use of 50 ppm Borates can also help (this was first figured out in this thread). 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 and Taylor K-1592. 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 can be used to calculate dosages, but for moving the pH these calculations are approximate. I have the accurate calculations in the Pool Equations 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 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.