TA, CYA, and minor staining

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
rmiller111
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TA, CYA, and minor staining

Postby rmiller111 » Fri 10 Aug, 2007 09:30

I recently installed an inground pool, and filled it with well water and my total alkalinity is pretty high. I've already bought muriatic acid and expect to follow the procedure posted here to lower it, but based on some of the comments, it may not be necessary.

Last night I bought a six way test here are the results.

FC - 2
PH - 7.2
TA - 220
Hardness - 250
CYA - <30

I only filled the pool about 12 days ago, and did the initial testing 7 days ago. The pool guy who helped with the construction process added some PH lowering after the initial tests came back at 7.8. I ran the pump through filter for 2 days, then did the initial shock based on his instructions. I then turned on the auto chlorinator to a setting that he recommended.


The water looks perfect and the temperature is already at 84. The water bugs that initially were seen, have all been caught in the strainers (how did they get there anyway?)

I've been testing the Free Chlorine every day, and its gone from above 3 after the shock(Sun.) down to 1 by Wed, I adjusted the auto chlorinator, and the FC is back up to 2.

Since I seem to be holding chlorine pretty well, I'm wondering if I should wait to see how the pool behaves in the next few weeks before messing with the TA.

Also, I have only minor discoloration of some of the plastic parts around the skimmer, light niche. It's a light yellow or brown, vs. the bright white, but again, its very minor. Is this the type of stain that would require Ascorbic acid treatments, or more drastic chelation?

So, the questions are:

1. Should I attempt to lower TA, wait, or forget about it?
2. Is my CYA level too low, or should I leave that alone too?
3. Thoughts on the staining?

Thanks,


Rob
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Postby chem geek » Fri 10 Aug, 2007 13:24

The high TA is only a problem if you find the pH rising or if you intend to keep the pool above 7.4 or so in pH since it will have a tendency to scale if the pH rises too much. Since your pH is low, I suspect you are using Trichlor pucks in your automatic chlorinator, is that right? If so, realize that for every 1 ppm Free Chlorine (FC) added by the Trichlor, it also adds 0.6 ppm to Cyanuric Acid (CYA). Unless you have a lot of splash-out and backwashing and a smaller (< 10,000 gallon) pool or a short swim season or use a pool cover to keep out the sun's UV rays, then you will likely have your CYA rise over time.

You will need to raise your FC level as the CYA level rises unless you use a weekly maintenance dose of PolyQuat 60 algaecide. The FC level target should be 11.5% of the CYA level and certainly should never get below the minimum of 7.5% of the CYA level unless you use the algaecide (in which case just keep a 3 ppm FC level regardless of CYA until the CYA gets to 150 ppm at which point you'll need to drain/refill to lower it anyway, especially if you have a plaster pool).

As for the CYA level, 30 ppm is OK unless you have a lot of direct sunlight. See how your FC drops during the day. If it drops more than 40% of its initial value on a day when you aren't using the pool, then you can try raising it to 50 ppm, but as stated above it will rise on its own if you are using Trichlor pucks.

You can prevent the rise in CYA by using unscented bleach or chlorinating liquid instead of the Trichlor pucks (and instead of Cal-Hypo which raises calcium hardness). If you want to automate its introduction rather than having to add it every day or two, you can get The Liquidator to automatically add the chlorine to the pool.

I'm not sure on the staining of the plastic -- it does sound like it might be metal staining so you can have your pool water tested at a pool store for metals (iron, copper) and then do an ascorbic acid and sequestrant treatment. Since the ascorbic acid requires the chlorine to be very low (FC < 1 ppm), you should add the PolyQuat 60 algaecide before doing that treatment to ensure you don't get algae while treating for the stain.

Richard
rmiller111
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Joined: Fri 10 Aug, 2007 09:11
Location: Kalamazoo, MI

Postby rmiller111 » Mon 13 Aug, 2007 09:19

Thanks Richard,

This is a vinyl lined pool, and I am using trichlor pucks in an auto chlorinator. The pool is approx. 23K gallons, and I've gone through 10 pucks in the first week. So I can see how after a year or two the build up of CYA could be a problem. I am using EZ Chlor Algeacide Plus ( a 60% polyquat) so I think I'll follow my weekly maintenance plan and just test for cya once in a while. I've been putting in about 5 oz. once a week.

I did do a half gallon of muriatic acid to see the effects. I have been running a oscillating sprinkler around the pool to settle the sand backfill in preparation for the pouring of the deck. The PH did rise to ~7.8 (I think, its hard to read the red shades in the window), so I took the opportunity to try a half gallon of muriatic acid. The TA did go down approx. 20 ppm and the PH went right down to 7.2. I think if I keep running the sprinkler to raise the ph and settle the sand, I can probably get the TA down to 150 before the deck is poured.

Regarding the stains, they do not seem to be getting worse, and I do use the EZ Clor Super Shimmer and shine, although I don't think this is a sequesterant treatment.

What do you recommend as a sequesterant treatment? Is it a weekly type maintenance or a once in awhile treatment?
Rob
chem geek
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Joined: Thu 21 Jun, 2007 21:27
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Postby chem geek » Mon 13 Aug, 2007 10:51

For every 1 ppm Free Chlorine (FC) added by Trichlor, it also adds 0.6 ppm to Cyanuric Acid (CYA). So if you don't have a lot of splash-out or backwashing of a filter, then it's very easy to have the CYA build up a LOT in just one season. If you only added 1 ppm FC per day (which would be low since usually daily usage is more than that) then after 6 months this would be 6 * 30 * 1 * 0.6 = 108 ppm added to CYA.

So having a cartridge (or some DE) filter that doesn't get backwashed can have the CYA rise quickly. This happened in my own pool when I first got it even though I had an opaque pool cover and only had chlorine consumption of around 0.5 - 0.7 ppm. My CYA was well over 100 ppm after a year and a half ("summer" swimming season is around 7 months). In a pool without a pool cover, one could easily get to higher CYA faster.

Note that evaporation does not dilute CYA since it just concentrates the CYA and fresh water brings it back to the same concentration. Only physical removal of the water dilutes the CYA.

So depending on your specific situation, you should test your CYA again after a few months to see where it's at and remember that if you don't keep your Free Chlorine (FC) level at a minimum of about 7.5% of the CYA level (typical target level is 11.5%), then you risk getting green algae (mustard/yellow algae can require a higher 15% level to keep away, but that algae is less common). If you don't want to worry about your CYA level, then you should either use a weekly maintenance dose of PolyQuat 60 algaecide or use a phosphate remover (they're expensive, but aren't used as frequently as an algaecide).

As for metal stains, read this post . I don't have specific recommendations for the metal sequestrant and it appears that most work effectively and are sold under a variety of brand names. It's mostly a one-time application unless you refill the pool with well water or other water that contains metals (including filling to make up for evaporation).

Richard
rmiller111
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Joined: Fri 10 Aug, 2007 09:11
Location: Kalamazoo, MI

Latest status

Postby rmiller111 » Thu 23 Aug, 2007 09:03

After adding another 1/2 gallon for a total of 1.5 gallons of m. acid, the Total alkalinity has gone from 220 to 130. I've done it over 3 weeks time, and everything seems pretty stable.

I use trichlor pucks, so I may add the last 1/2 gallon, as the PH still is creeping up. We've received a lot of rain around here, as most of the midwest, so it's back up to 7.5, and at that point, the half gallon gets it down to the 7.2 anyway.

I've started using the solar cover, so that should prevent some the of PH rise because of aeration.

Thanks for all the assist.

R. Miller
Rob
chem geek
Pool Industry Leader
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Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Postby chem geek » Thu 23 Aug, 2007 12:47

And rain aerates the water with its splashing drops. In pools that have a tendency for the pH to rise, most people find that it happens more rapidly during rain.

You should find that the tendency of the pH to rise from a starting point of 7.5 is less than it was before and the amount of acid needed to restore the pH will certainly be a lot less. Trying to keep the pH lower than 7.5 will be harder. At any rate, you can continue to lower the TA level until things get more stable.

And let us know how things go after putting on the cover. As you say, it should reduce aeration so should reduce pH rise -- in fact, you may see pH drop due to use of the Trichlor.

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