Low PH

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
barhip

Low PH

Postby barhip » Sat 08 Sep, 2007 18:04

i am still battling the problem of not being able to increase the ph level in my pool. i finally attained the level of ta i needed - 130 ppm. a 25000 in ground vinyl lined pool. using tri-chlor tablets.
i have been running some aeration all week for a couple hours at a time - we used a sump pump in the pool and let it fall in the deep end. i have turned the chlorine level to the lowest setting not quite off on the chlorinator.
today i added 12 lbs of this 20 lb mule team borax you mentioned. i waited for 2 1/2 hours - continued to aerate the pool. checked levels again and the ta increased to 160 and no change in the ph - still reading the lowest level of 6.8. we want to close our pool this week but i am concerned about leaving the ph that low for the winter. i don't know what else to do - i have tried everything. HELPPLEASE


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Postby chem geek » Sat 08 Sep, 2007 20:37

Trichlor is VERY acidic so a lot of its use probably had the pH very, very low. So I suspect that you are almost there, but all you can tell for sure is that the pH is 6.8 or lower.

The good news is that since your TA test did not immediately turn red (i.e. you counted 13 drops), so your pH is definitely above 4.5 (some pools that use only Trichlor and don't adjust the pH get down to 4.0 or even lower, which is very corrosive).

When you say you finally attained the TA level you needed, and then said "using Trichlor tablets", do you mean that you only added Trichlor tabs until you measured a 130 ppm TA? Or did you add Alkalinity Up (Baking Soda) to raise the TA? Do you know your pool's Cyanuric Acid (CYA) level?

12 pounds of 20 Mule Team Borax in 25,000 gallons isn't going to raise the pH by very much. If the pH were at 6.5, for example, then that would only raise it to 6.64. Remember that it takes about twice as much Borax by weight to move the pH the same amount as pH Up.

Unless your CYA level is sky high, you can use your chlorinator to do aeration as well. I'm not sure why you turned it down so much -- is that because the chlorine level is high enough and easily maintained this time of year? Also, keep in mind that very high chlorine levels will influence the pH test -- usually making it look like the pH is higher than it really is (not the problem you have).

If your pH is at 6.5, then to get to 7.5 would take almost 12 boxes of (76 ounce per box) 20 Mule Team Borax. If the pH is just at 6.8, then it would take 5-1/2 boxes. So why don't you just add 6 boxes and then see if the pH measures above 6.8. If it does, then you can use aeration to get the rest of the way there unless you are in a hurry in which case you can use more Borax.

I think it would be a good idea, after your pH is adjusted, to post a full set of numbers, including FC, CC, pH, TA, CYA and possibly CH though the latter isn't important for a vinyl pool.

Richard
barhip

Postby barhip » Sun 09 Sep, 2007 10:59

ok - i was just informing you that i use trichlor tabs so the normal range for my ta s/be 120-140. so 130 was good - the way i got it DOWN - not up - was muriatic acid - 3 gallons. so after i attained the 130 level - that is when i put in the borax. after re-testing - the ta went up to 160. so the borax did raise the ta.
next point you raise - quanitity of borax - if i add that much it wil make the ta go back up to an unacceptable range.
the cya level is fine - i took our water to a pool store and had it tested. they confirmed my findings - too high ta and too low ph. she mentioned the ta being that high can give you a false reading on the ph - is that true?
next point - i turned the chlorinator down to low because the chlorine level is fine and i thought that it would help since the trichlor tabs tend to be acidic. i still don't get how the ta can get so high if this type of chlorine tabs tends to be acidic.
finally - how can you aerate the pool with the chlorinator? can't figure that one out.
thanks again for your help - it is really nice to be able to have some input from someone who is not trying to sell you products.
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Postby mr_clean » Sun 09 Sep, 2007 11:47

If your pH is at 6.5, then to get to 7.5 would take almost 12 boxes of (76 ounce per box) 20 Mule Team Borax. If the pH is just at 6.8, then it would take 5-1/2 boxes. So why don't you just add 6 boxes and then see if the pH measures above 6.8. If it does, then you can use aeration to get the rest of the way there unless you are in a hurry in which case you can use more Borax.

Chem geek is saying to get PH to 7.5 and then start TA adjustment again. Once you get PH at 7.5 you add acid so PH goes to 7.2 so PH can be aerated back up. With TA 6.8 it does not work good. When aerating PH back to 7.5, TA stays down.
Also he wants chemical readings to see where your at.
With chlorine tabs being used CYA levels tend to rise to high and can give false readings to TA. If your TA is 100 you would divid it by 3 and subtract from reading.
example CYA 100 & TA 130, 3 div 100 = 30 sub 130 = 100
If CYA is above 100, drain some water from pool to lower and get in to range.
PH readings would be bleeched and false like chem geek stated from high chlorine level.
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Postby chem geek » Sun 09 Sep, 2007 14:09

Thanks for the clarification. I didn't realize you were adding acid to lower the TA level. When the pool store said the CYA level was "fine", what level was it? They might say it's fine up to 100 but that's pretty high.

If I use a CYA of 100 and start with a TA of 200 and pH of 7.5, then add 3.5 gallons of Muriatic Acid to the 25,000 gallon pool, I end up with a pH of 6.5 and a TA of 130 so I'm guessing that something like that may have been what you did originally (you didn't say the starting TA number).

I'm sorry that I misunderstood what you meant by Trichlor and using a chlorinator. I now understand that this is an inline Trichlor chlorinator, not a saltwater chlorine generator (SWG). My comment on using the chlorinator for aeration would apply to an SWG, NOT to your Trichlor chlorinator. Sorry about the misunderstanding.

The Borax does not increase the TA by very much "extra" beyond the way TA climbs when one increases pH. pH and TA move together, but using a pH Up product adds "extra" to the TA -- it's like adding Borax plus Alkalinity Up together. If I start with a pH of 6.5 and TA of 130 and then add 5.3 boxes of Borax, then I get to a pH of 6.8 and TA of 160. You didn't add that much Borax, but it gives you an idea of how the pH and TA move together.

As mr_clean says, the high TA will not give you a false reading on the pH, but a high chlorine level will. Above 5 ppm FC the pH test starts to be affected and above 10 ppm FC the pH test will usually look as if the pH is higher than it really is. This is not your situation, however.

As for how the TA got high in the first place, it's probably because you added pH Up products to raise the pH to compensate for Trichlor lowering the pH. As I said, pH Up is sodium carbonate and is equivalent to adding a pure base (such as Lye, though Borax is somewhat similar) and Alkalinity Up (sodium bicarbonate). So if you regularly use pH Up to adjust for pH when using Trichlor, the TA will climb to some level where it is balanced against the outgassing of carbon dioxide from the pool. Keeping a pool covered or otherwise having less aeration in the pool will tend to have the TA go up higher. The way to avoid this is to not use pH Up to raise the pH, but to use a combination of aeration and/or Borax and/or Lye.

HOWEVER, continued use of Trichor will make the CYA get too high and this makes chlorine less effective so that you need to raise the FC level to compensate (or you need to use an algaecide, such as PolyQuat 60 weekly, to prevent algae). So unless you do a regular partial drain/refill, the CYA level will climb. The way around that is to use a different source of chlorine. Cal-Hypo won't add to CYA but will increase Calicum Hardness (CH), but that's not as much of a problem, at least for a while unless your fill water is already high in CH. Unscented bleach or chlorinating liquid will not add to either CYA nor CH. With any of these manually added products, they must be slowly added over a return flow the pump running (and for Cal-Hypo especially, should be pre-diluted in a bucket of pool water) and they need to be added frequently -- every day or two depending on how much sun hits your pool. These hypochlorite sources of chlorine are actually pH neutral when accounting for chlorine usage so a lower TA is better for such sources to reduce a tendency for the pH to rise, but that's something that can be dealt with later AFTER you get your pH in the normal range.

Just add more Borax and don't worry about the higher TA right now. The higher TA is NOT a problem for your pool unless the Calcium Hardness (CH) level is normal-to-high (and with a vinyl pool you didn't need CH to be at 300 -- did you have that measured?). It is a combination of pH, TA and CH that determine whether your pool is over-saturated with calcium carbonate and will become cloudy or precipitate scale. So if you CH is low, then your TA can be higher with no problem (at least when using an acidic source of chlorine such as Trichlor). I suggest you take charge of your pool and get yourself a good test kit, the Taylor K-2006 from Taylor here or from Leslie's here or from poolcenter(dot)com here or the even better TF100 test kit from tftestkits(dot)com here .

When you have a complete set of pool water chemistry numbers that you know are accurate because you've done them yourself, then it's easy to make adjustments and stay in balance.

Richard
barhip

Postby barhip » Mon 10 Sep, 2007 17:33

thank you so much for all of your information. i did add the additional borax and a little ph plus and my ph is finally 7.2. i am still uncovering the deep end and aerating. the ta is 150. i am going to get a better test kit so i can measure all of those items you mentioned.

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