Low Ph and High Ta

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
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Joined: Wed 06 Jun, 2012 12:45
My Pool: Use: Medium-sized townhome community pool.
Size: 40' x 20'
Depth: 3' to 6'
Filter: Sand
Location: Minneapolis, MN

Low Ph and High Ta

Postby csever82 » Wed 06 Jun, 2012 14:00

This is my first post here, so please bear with me. Under the guidance of a licensed pool operator, I take care of the in-ground pool for the townhouse community I live in. Last year, I only had to deal with the chemicals while the regular operator was out of town...the rest of the time, I just plugged in the vacuum and locked up the pool area every night.

Now I have been "promoted" to taking care of the pool alone every day. Although the water looks great most of the time, I have learned quickly that accurate chemical adjustments are really vital vs. the method I was taught. Basically, I was shown how to do things in nondescript quantities like buckets, scoops, and bottles rather than ounces or pounds.

Problem: High-ish total alkalinity with constantly dropping pH and limited options for correction.

Here are my test results from this morning using a Taylor K-2006 kit:
FC: 3.0
TC: About 4.0
pH: 7.0
TA: 190
CH: 225
CYA: Unknown

My pool: 40 x 20 feet, average depth 4.5 feet, not sure what surface (I think concrete)
Pool chemicals: Combination of chlorine pucks and granular chlorine, soda ash, cyanuric acid
My pump & filter: Pump has a deep end skimmer, shallow end skimmer, and two main drains; sand filter
Other info: Pool has a flow rate of only about 85 or 90, which is low from what I've been told, but that's because the pump from a previous, smaller pool was salvaged and used on this one. I live in Minnesota, so the pool is open generally Memorial Day weekend through mid-September. The pool is heated to 82°F. It is used heavily every day unless it's raining and/or the air temp is maybe less than 70°F - so in other words, it is rare to find it has not been used heavily all day long. The pool is open 12 hours each day, from 9 a.m. to 9 p.m.

Basically, I used about 10 lbs. of cyanuric acid to lower the TA, which started out at about 220. But it only came down to 190. Meanwhile, the pH drops continuously. I have already used an entire 30-pound bag of soda ash just to keep it at 7.0 to 7.2, and the pool has only been open for a week and a half.

I have read conflicting information regarding the TA as it relates to pH. Some say my TA is high but not high enough to worry about, and one of these people is the guy who "taught" me how to take care of the pool...and he's in charge of ordering the chemicals. He says the acid to lower TA is too expensive to get too much of it, but most of the information I've read indicates that if I can get the TA under control, my pH won't keep declining all the time. I also have no way (that has been provided to me, anyway) to aerate the pool, and I can't find anything in our complex's shop that would help me do so.

So my question is this: should I take up the issue with the property manager directly and just let her know that I need this stuff in order to get everything correct in the pool, or should I just keep going through what seems like large amounts of soda ash to constantly correct the pH? Is my TA too high? Or high but not bad? Also, on a side note, does anyone have any tricks for fixing slightly cloudy water quickly? Usually, the pumps fix that overnight, but once in a while, it's like they can't quite keep up with the bather load or something. The water doesn't turn into milk, but occasionally I can't see the drains really clearly...and I prefer the water to be clear enough to see them from the shallow end. Is time the only solution there (closing the pool for a day every couple weeks or something)?

Please help!!

chem geek
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Low Ph and High Ta

Postby chem geek » Wed 06 Jun, 2012 19:37

Please tell me that you didn't really use "about 10 lbs. of cyanuric acid to lower the TA". You use Muriatic Acid, which is a liquid so measured in cups or gallons, or perhaps you use dry acid (sodium bisulfate) which could be measured in pounds. You do not use Cyanuric Acid (CYA) to lower TA.

I suggest you read the Pool School to learn more about how to manage the pool. Your low pH comes from your use of Trichlor pucks and possibly also from granular chlorine if it was Dichlor (was it? Or was it Cal-Hypo?). Trichlor is very acidic while the soda ash raises both pH and TA so it is not surprising you have both low pH and high TA if your water does not get a lot of aeration. With your relatively high TA level one would normally expect the pH to not drop so much, but it's certainly possible.

You really need to get yourself a proper test kit, either the Taylor K-2006 or the TFTestkits TF-100. This will tell you your Cyanuric Acid (CYA) level which I suspect is high because of the following chemical facts that are independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

You can use The Pool Calculator to help you figure out chemical dosing. You should also be using more chlorinating liquid or 6% bleach though in the short-run you can use some Cal-Hypo since your CH is low if you do end up lowering your TA -- it's OK to have the TA be high where it is given the lower CH level and not having the pH rise (you've got the opposite problem now).

As for cloudiness, it could be algae starting to grow that then gets killed off when you add more chlorinating granules. If it's instead things like suntan lotion, then you need better filtration and better oxidation of bather waste. If your CYA is too high, then that could contribute to the problem since it lowers the active chlorine (hypochlorous acid) level. If you don't mind spending extra money, you can use Polyquat 60 weekly which is both an algicide and a mild clarifier, but if you properly maintained the appropriate FC level relative to your CYA level, then you shouldn't need it.

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