Bleach VS Tabs

First of all, I would like to thank this forum for all the good information that I have found here. Perhaps the most important thing, was to buy a GOOD tester to keep track of your pool's chemistry. I had been having an issue with mustard algae, probably because of a very high CYA level and not having enough available chlorine. I dumped about half of the water out and got my CYA level down to about 60. (I didn't have the new test kit before I dumped the water but I imagine it was around 120) The pool is 30 years old and had never been emptied. Most of those years, trichlor tablets were used.

After reading about the popularity of using bleach, I thought I would try it. Here is my experience. I started keeping rather detailed records of the water's chemistry, checked the chlorine, combined chlorine, ph, and water temp. every day. Checked the total alkalinity, calcium hardness, cya, sat. index every month.

I am trying to keep my chlorine level between 5 - 10 ppm & ph 7.6 - 7.8. given my numbers:
15,000 gal in ground pool fiberglass walls/gunite bottom. 1.5 hp pump running 9 hours per day (4 hour break in the afternoon). Water sparkling, no algae, bottom plaster flaking off, needs to be redone.

Total Alk. 110 / Ca hard. 190 / CYA 60 / Sat. Index +0.2 / water temp 82f - 90f (depending date & time of day.

When using bleach, I was using about nine 96oz bottles per week to maintain a good level. I used bleach for over one month. After some mental math, I felt something was wrong, so I switched back to tri chlor tablets and continued keeping detailed records. I found that I was using four tablets per week. Here is a break down on weekly costs:

(9) 96oz bottles = $13.50 / (4) tablets = $6.72

This is based on an average price of $1.50 per bottle of bleach (has gone up in the past few weeks)
Tablets cost $1.168 each. (based on 40lb bucket @ $90 / each tablet weighs 8.3oz - 77 tablets in bucket - calculated)

I also calculated the amount of tablets (in oz.) used by weighing the remainder of each tablet, every morning at the same time. The chlorine level dropped slightly as the tablet grew smaller in size. (this could be eliminated by replacing the two tablets on different days)

My impression of using bleach was:
I was having to cart a lot of bottles every week from the store and using up a lot of space to my trash can every week. (we currently don't have a recycling program here) The weekly transporting and storage was a pain.

My chlorine level was varying between 3.5 - 10 and was having trouble keeping it a stable level (especially during the day)

I started using a lot of acid to maintain a proper ph. I presume from the use of the bleach. (according to the booklet in the test kit)

Although all the bleach purchased was "6%" I suspect some purchased from Target, may have been lower or perhaps old because of the small amount it raised my chlorine level. Not impressed by the quality control of bleach.

After I switched back to the tablets:
I only went out twice a week to drop 2 tablets into my skimmers instead of more than one a day with bleach.

My chlorine level became very stable (7.5 - 8.5ppm)

I stopped having to use acid ( 7.7ph stable over the last week) Saved money on acid, as well as the hassle of dealing with the stuff.

I'm not trying to start an argument about the virtues of bleach, just wondering if I am missing something (or doing something wrong) in the "bigger picture?"

Thanks again for the good information.

9 bottles per week especially with a CYA of 60 is a lot. My pool isn't too much smaller than yours (13,500 gallons or so) and my CYA is probably around 35 and I use about 4 bottles per week.

If you lower your TA to about 80 ppm when using bleach or ANY unstabilized chlorine source then you will find that your pH would be stable. Your TA was too high! The MAIN cause of pH rise in swimming pools is from outgassing of CO2. By lowering TA your slow the outgassing and the pH rise. Tabs are very acidic so, in effect, you are adding chlorine, stabilizer, and acid all at once. The constant acid addition causes TA to drop so you have to set the TA higher then when you are using an unstabilized chlorine source. Unstabilized chlorine sources, inscluding bleach, are basically pH neutral. The are alkaline when added but the reduction of hypochorite to chloride (which is what happens when the chlorine is 'used up') is an acidic reaction so the net effect is pH neutral. Trichlor and dichlor (the two stabilized chlorine sources used in pools) are acidic when added (trichlor quite acidic in fact) and the same acidic reaction takes place when the chlorine is consumed so the net effect of use is acidic. This means you never need to add acid but you do need to monitor TA and pH closely and adjust as needed and maintain the TA at a higher level so it will drive the pH upward faster to compensate for the 'acid' added by the trichlor.

If you were adding 9 (96 oz) bottles of 6% bleach per week then you were adding about 28 ppm FC weekly. This is a 4 ppm FC loss per day which I find hard to believe with 60 ppm CYA in the water. It means you were fighting some sort of algae bloom that would have been quickly taken care of by just shocking the pool.
On the other hand your 4 (8.3 oz) trichlor tablets would mean you are adding only 15 ppm FC weekly, about half of what you were supposedly adding in bleach but you are also raisng the CYA by 9 ppm weekly and dropping the pH by .8!!!! (That is a lot of acid!).

The numbers just do not add up so I would have to say your experiment is a failure either because of inaccurate testing, improper dosing, or some other error on your part. It has been documented time and again that bleach is more cost effective than trichlor.

If you added bleach and the FC did not rise I would suspect a nascent algae bloom or something growing in a hidden area of the pool. Your chlorine demand was just too high to be normal. I also find it hard to believe that there were no problem when you added half the amount of chlorine with trichlor weekly since you were causing the CYA to rise once again.

Thanks for the insight, it will give me a few things to check. A few questions:

To lower TA, I will need to add acid. I understand then, to raise the PH back up, you need to aerate. What is the best way? I don't have any fountains etc. Rig some tubing into the return lines, pointing up? If the water is low, the returns will cause some surface "rippling" but I wouldn't compare it to a "fountain."

If I understand, if I want to continue to use the tablets, my TA is fine, at it's current level?

My confusion about acid demand came from the Taylor Test kit manual, page 21:
"Disadvantages (bleach)... (the) most alkaline chlorine sanitizer; significant acid demand..." Your thoughts?

I did shock the pool when using bleach 3 weeks ago. I suppose it's possible that the shock killed "something" which would explain my lower chlorine demand. I started using the tablets about 2 weeks ago.

I'll check the CYA in the morning and see where it's at. (Haven't checked it since 9/1)

Thanks again

Quote:

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Originally Posted by waterbear

If you lower your TA to about 80 ppm when using bleach or ANY unstabilized chlorine source then you will find that your pH would be stable. Your TA was too high! The MAIN cause of pH rise in swimming pools is from outgassing of CO2. By lowering TA your slow the outgassing and the pH rise. Tabs are very acidic so, in effect, you are adding chlorine, stabilizer, and acid all at once. The constant acid addition causes TA to drop so you have to set the TA higher then when you are using an unstabilized chlorine source. Unstabilized chlorine sources, inscluding bleach, are basically pH neutral. The are alkaline when added but the reduction of hypochorite to chloride (which is what happens when the chlorine is 'used up') is an acidic reaction so the net effect is pH neutral. Trichlor and dichlor (the two stabilized chlorine sources used in pools) are acidic when added (trichlor quite acidic in fact) and the same acidic reaction takes place when the chlorine is consumed so the net effect of use is acidic. This means you never need to add acid but you do need to monitor TA and pH closely and adjust as needed and maintain the TA at a higher level so it will drive the pH upward faster to compensate for the 'acid' added by the trichlor.

If you were adding 9 (96 oz) bottles of 6% bleach per week then you were adding about 28 ppm FC weekly. This is a 4 ppm FC loss per day which I find hard to believe with 60 ppm CYA in the water. It means you were fighting some sort of algae bloom that would have been quickly taken care of by just shocking the pool.
On the other hand your 4 (8.3 oz) trichlor tablets would mean you are adding only 15 ppm FC weekly, about half of what you were supposedly adding in bleach but you are also raisng the CYA by 9 ppm weekly and dropping the pH by .8!!!! (That is a lot of acid!).

The numbers just do not add up so I would have to say your experiment is a failure either because of inaccurate testing, improper dosing, or some other error on your part. It has been documented time and again that bleach is more cost effective than trichlor.

If you added bleach and the FC did not rise I would suspect a nascent algae bloom or something growing in a hidden area of the pool. Your chlorine demand was just too high to be normal. I also find it hard to believe that there were no problem when you added half the amount of chlorine with trichlor weekly since you were causing the CYA to rise once again.

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Quote:

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Originally Posted by samtex

Thanks for the insight, it will give me a few things to check. A few questions:

To lower TA, I will need to add acid. I understand then, to raise the PH back up, you need to aerate. What is the best way? I don't have any fountains etc. Rig some tubing into the return lines, pointing up? If the water is low, the returns will cause some surface "rippling" but I wouldn't compare it to a "fountain."
IF you drop the pH to 7.0 (if you have a Taylor K-2005 or K-2006 I like to use the acid demand test to do this) and just wait the pH will rise as CO2 outgasses but it will take a longer time than if you aerate. Analogy: Your pool is carbonated just like a bottle of club soda. This is the bicarbonate in the water we csll TA. The higher the TA the higher the carbonation. Adding acid to the pool converts some of the bicarbonate into carbonic acid (operative word here is acid). Carbonic acid is basically CO2 dissolved in water. Now if we just let our bottle of club soda sit open it will go flat (CO2 will outgas) but if we shake it (aerate) it will go flat much faster. As the CO2 outgasses the amount of carbonic acid (which is CO2 dissolved in the water) decreases. Operative word here is acid--The amount of ACID in the water decrease and therefore the pH rises.
The act of adding the acid is what lowered the TA (decreaed the amount of bicabonate in the water by converting it into carbonic acid--the "fizz" in our club soda.) Letting the CO2 outgas (letting the club soda go flat) brought the pH back up because we had less carbonic ACID left in the water (operative word is acid). Shaking the bottle of club soda just speeds up the process, given enough time the club soda would go flat on it's own and so will your pool.

However, anything that moves the water and breaks the surface will aerate. One of the best ways is to invest in one of those small flaoting fountains that attaches to a return. They are not expensive at all. Others have made "fountains" out of pvc pipe and a 90 degree union to shoot the water into the air so it falls back into the pool and I have heard of using people using an air compressor as a giant "aquarium airstone" by submergng the hose and letting it bubble through the water.
Here is PoolDoc's step by step guide.

Here is a more detailed and advanced guide that I wrote for a different forum but the process is identical.

If I understand, if I want to continue to use the tablets, my TA is fine, at it's current level?
Yes, you need to maintain a higher TA when using trichlor and dichlor. I like to keep the TA at least 100 PPM as a bottom limit and as high as 150 ppm as an upper limit. In CPO courses (certified pool operator) they give a guideline of 100-120 ppm when using stabilized chlorine (and other acidic sanitizers/oxidizers like bromine and MPS) and 80- 100 ppm for unstabilized chlorine. This is one of the things they got right!
My confusion about acid demand came from the Taylor Test kit manual, page 21:
"Disadvantages (bleach)... (the) most alkaline chlorine sanitizer; significant acid demand..." Your thoughts?
They are only giving you half the story!
AS I said, it is alkaline on addition but the chemical reaction it udergoes when it sanitizes is acidic so the net effect is pretty close to pH neutral and the primary cause of pH rise in pools is outgassing of CO2. While the Taylor test kit is excellent the book that comes with is contains several inaccuracies that are so widespread in the pool/spa industry that it is a very difficult process to get them to disappear. PoolDoc even has a name for these inaccuracies--TEKTAT--Things Everybody Knows That Aren't True.
I did shock the pool when using bleach 3 weeks ago. I suppose it's possible that the shock killed "something" which would explain my lower chlorine demand. I started using the tablets about 2 weeks ago.

I'll check the CYA in the morning and see where it's at. (Haven't checked it since 9/1)

Thanks again

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No problem.

Evan's guidance is good.

I will add three things: 1) You said your pool bottom is gunite and flaking and your calcium level is 190ppm. That's below the suggested range of 200-400ppm. I suggest you raise it.
2) There is a little fountain for about $20 that screws into your return instead of the eyeball. It can raise pH at a PRODIGIOUS rate via aeration.
3) If you buy 12% Liquid Chlorine in 5 gallon carboys with a spigot you can use to pour off the LC, and just reuse your empty bleach bottles, you'll twice the "bang" from each bottle. Your only recycling will be to bring the empty carboy back to exchange when you get a new one.

There's nothing fundamentally WRONG with using Trichlor tablets IF you use them correctly.

Carl