Question about total alkalinity

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

Postby clgasg » Mon 21 Apr, 2008 19:20

To start I have a 27'x52" above ground vinyl liner pool (17,500 gallons). I had it installed last July and have had nothing but crystal clear water. Opened it this year and this is now my readings.
Sat index:-.7
TDS:300
CYA: 21
Tot chlor:5.5
Free Chlor:5.5
PH:7.0
Tot Alk:89
Adj Alk:83
Total Hard:251

Now my local pool dealer is telling me to add 11.5 lbs of Balance pak 100 to increase the total alkalinity to 125-150. He said that this should also help the PH. Question is my test kit says that the Total alk is fine at 89, the range for it is 80-125. I have also saw conflicting info that 80-125 is normal for plaster, gunite, or concrete, but 125-150 is normal for vinyl and fiberglass.
What do I need to do?????
Thanks in advance,
Chris


chem geek
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Total alkalinity pool care

Postby chem geek » Mon 21 Apr, 2008 21:24

Assuming the numbers from your pool store are correct, the first thing to do is to raise the pH, not the TA. Though the pool store is correct that raising the TA will also raise the pH somewhat, you are also correct that your TA does not need to be higher (except for some conditions I'll get to in a moment). If you were to follow his advice and add 11.5 pounds of Balance Pak 100 (which is just sodium bicarbonate and is identical to Arm & Hammer Baking Soda), then this would raise the TA to 136, but would only raise the pH to 7.17

If instead you use pH Up or Balance Pak 200 (which is sodium carbonate and is identical to Arm & Hammer Washing Soda -- careful: not the detergent), then 3.5 pounds in your 17,500 gallon pool would raise the pH to 7.5 and the TA to 112.

If you want to raise the pH without raising the TA as much, you can use 6.9 pounds of 20 Mule Team Borax which will raise the pH to 7.5 and the TA to 101.

If you want to raise the pH with no change in TA at all, then aerate the water.

All of the above assumes you aren't adding anything acidic to the water. What kind of chlorine have you been using? Your low CYA would indicate that you might be using Cal-Hypo granules though your Calcium Hardness (that I guess at 157 ppm) isn't very high. I am very surprised that your pool store tested for Total Hardness instead of Calcium Hardness.

On the other hand, your low pH may indicate that you had used Trichlor pucks/tabs in the previous season and closed the pool to low pH. So again, what have you used as your source of chlorine in the past?

Richard
clgasg
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Total alkalinity pool care

Postby clgasg » Mon 21 Apr, 2008 21:53

I had been using a brand of 3" chlorine tablets from Walmart because I thought they were cheaper. Only had a pool since July so I have to plead ignorance.
Now I have Pool Life 3" stabilized chlorine tabs to use this season. Unless the shock has stabilizer in it, I didn't put any in last summer. The only thing I did this year was use In The Swim's start up kit.

If I am understanding you correctly, I just need to raise the PH to around 7.5 and forget about the Balance Pak 100. By the way I do have stabilizer to put in to get it within normal limits, I just figured that I better get this straightened out first.
chem geek
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Total alkalinity pool care

Postby chem geek » Mon 21 Apr, 2008 23:28

The 3" tabs from Walmart were probably the same as the 3" Pool Life stabilized tabs. Both are Trichlor and for every 10 ppm Free Chlorine (FC) that they add, they also add 6 ppm to Cyanuric Acid (CYA). If you want to use those tablets, then you can do so and the CYA level will rise over time. You probably don't need to add any right now as your use of these tabs will add more CYA.

I'm not so sure I trust the pool store numbers. You should get a good test kit such as the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits(dot)com here which has 36% more volume of reagents so is comparably priced per test.

Yes, you don't need the Balance Pak 100 and instead should use either Balance Pak 200 or Arm & Hammer Washing Soda (they are identical) in the amount I indicated. Since you are going to be using Trichlor, raising the TA to 112 should be fine for now.

If you continue to use Trichlor then the CYA will keep climbing unless you dilute the water. If you want to prevent algae growth, then you will need to keep the Free Chlorine (FC) level at a minimum of 7.5% of the CYA level (targetting 10% is easier). Raising the FC level over time may be difficult with Trichlor so you can instead use an algaecide such as PolyQuat 60 on a weekly basis (or use a phosphate remover) in which case you won't need to raise the FC level over time. Essentially, the CYA makes the chlorine less effective and it is the ratio of FC to CYA that determines the actual disinfecting and oxidizing chlorine level.

If you backwash your filter regularly, have lots of splash-out or rain overflow, have a smaller pool, or otherwise dilute the water, then the CYA level can be kept in check and you won't need to raise the FC level.

Another alternative would be to use unstabilized chlorine (after the CYA gets up to 30-50 ppm), but that requires more diligence since chlorinating liquid or unscented bleach would need to be added every day or two. The choice is up to you.

Richard
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Total alkalinity pool care

Postby Guest » Tue 22 Apr, 2008 07:28

After looking at the chlorine tabs that I had been using they actually are trichlor. Last season I used 1 3" puck every other day to every 3 days depending on rain and such. Does this sound normal?
chem geek
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Total alkalinity pool care

Postby chem geek » Tue 22 Apr, 2008 10:46

The 3" pucks vary in weight, but assuming it's the 8-ounce variety (they also come in 7 and 6 ounce versions), then one puck in 17,500 gallons would raise the Free Chlorine (FC) by 3.1 ppm and the Cyanuric Acid (CYA) level by 1.9 ppm. So with such usage every 2.5 days this is an increase in CYA of 23 ppm per month which is why I suspect that the pool store's measurement of CYA may not be accurate unless you had significant splash-out, rain dilution, weekly backwashing, etc.

At any rate, the pucks explain why the pH is low as Trichlor is very acidic. You would need to use pH Up (same as Arm & Hammer Washing Soda; careful: not the detergent) periodically to keep the pH normal.

So, it's up to you what to do, but if you want to continue to use Trichlor pucks, then to prevent algae as the CYA level climbs you'll need to use a supplemental algaecide (PolyQuat 60 or a phosphate remover) since you won't be increasing your FC level to keep up with the increasing CYA level. Get a good test kit as I indicated as that's the only way to know for sure what's going on with your pool. The pool store measurements are not always reliable.

If you decide you want to save money and use chlorinating liquid or unscented bleach (Clorox Regular or off-brand Ultra) instead, then you can automate this by using The Liquidator which you can read more about in this thread . You'd still need to buy and haul chlorine from the store and it's not as dense as Trichlor (so more weight to carry with the liquid forms of chlorine).

Richard

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