Pool using a lot of chlorine

Neal

Active member
Jul 12, 2012
28
0
SW Michigan
#1
I am new to TFP. I have been googling pool topics, which led me to this forum. I have read the "pool school" twice. I have a gunite pool that was built 10 years ago. Details are in my signature below. We have had very few problems and no major issues with water over the 10 years, but last summer our chlorine useage was up and it is even higher this summer. I decided to take control of this myself, rather than relying on the pool store, and my first step was to buy the recommended TF-100 test kit. It arrived yesterday and I have done my first tests.

As the topic states, my concern or problem is excessive chlorine use. As indicated in the signature below, I use tri-chlor tablets in a new water dispenser. I use Haviland di-chlor granules and liquid chlorine, as needed, which is every 1-2 days this summer. I do have ProTeam Supreme in the pool and have had for 5-7 years. I understand the CYA issue with tri-chlor and di-chlor, but I like the convenience of the New Water automatic dispenser. Simply stated, I am not at the pool daily to add liquid for the duration of the summer.

Here are my first test results from this morning, after adding 1.5 gallons of liquid and 5 cups of di-chlor granular at dusk last evening.

Free chlorine: 7.0 ppm
Combined chlorine: 1.5 ppm
Total chlorine: 8.5 ppm
PH: 7.2
Total Alkalinity: 145 ppm
Calcium Hardness: 290 ppm
CYA: 110 ppm
Borate: 30 ppm

Once again, although I have had the pool for ten year and I am fanatical about using the standard OTO/PH test, I am new to this level of detail. I am not a pool chemistry expert, but let me try my first analysis.

Chlorine: The free chlorine content is actually reasonable based on my CYA level. The problem is that is will be gone or very low by this evening. The combined chlorine indicates that I may have some bacteria in the pool since it should be near zero. I know that the sun eats the liquid chlorine during the day and the rest may be fighting some bacteria. The pool is and has been crystal clear, so there is no visible indication of bacteria or algae.

Alkalinity: This is a bit high. My undrstanding is that it can be reduced through aeration of the pool. I do have a fountain and waterfall that run constantly when we are in or around the pool. I have a jetted seating area that runs occasionally. I am not terribly concerned about alkalinity at this time.

Calcium hardness: Appears ok.

CYA: I know that this is high and I expected it since I use tri-chlor and di-chlor. I need to reduce it and I know that it is reduced by draining the pool. Since I live in a northern climate the pool is drained down about 12-18 inches each fall, but this is not enough. I have looked at the CYA calculator and it appears that I need to drain off 50%-65% of the pool and refill. I will do this, but would like to wait until September (when the grandkids are back in school, swimming slows and we stop heating). I fill the pool with our well water, which has a high iron/rust content. I know that adding 50-65% well water is going to cause some rust staining, which creates another issue. Any suggestions on reducing rusty well water would be appreciated.

Borate: Appears to be at the low end of OK. ProTeam Supreme is added at pool opening in the spring.

My summary analysis and plan:
Due to the free chlorine and combined chlorine test I think that I have some bacteria in the pool. The sun and bacteria are eating the chlorine daily causing it to disappear and creating my excessive chlorine useage. I understand that the high CYA adds to this problem. My solution is to shock the pool with liquid. The pool calculator shows that I need to shock with 7-8 gallons of liquid, getting the FC to 39 and then follow the guidelines for shocking. The Ph has been on the low side all summer, but adding this much liquid may increase it to the high normal range. Lastly, I need to drain and replace water to address the high CYA. I would really like to wait until September to do this and get the CYA down to about 50. I know that over time it will increase as long as I use tri-chlor in my New Water dispenser. I accept this as a trade off for the ease of maintaining chlorine and will need to drain water/refill periodically.

Sorry, for the long post, but this is my newbie analysis with the TF-100 results. Please, Please I would like and would welcome expert opinions on my analysis. Am I on track? Do you agree with my assessment. Do you have thoughts, comments, experience to set me straight?

Thanks,
Neal
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,446
0
SW Indiana
#2
I think you've pretty well got it other than worrying about pH rise with the shock. The pH will pretty well go back to here it was when the chlorine is consumed. Since pH tests are incorrect with high chlorine levels, don't worry about pH during the shock process.
 

Neal

Active member
Jul 12, 2012
28
0
SW Michigan
#3
Thanks for your reply John. So, I plan to move forward with the shock. I picked up 12 gallons of 12.5% liquid this morning. Our local big box store had a sale at $2.50/gallon. One question back to you, apparently you do not think that the high chlorine useage is simply because of the high CYA? By the way, our pool store tested CYA last mid-summer at 90 and last week at 90. My TF-100 last evening was 110 and I tested twice to be sure (since I am new at this). Lastly, when I say high chlorine useage this is what I mean. Last summer I used 6 new water pacs for the season, each lasting about 3 weeks and added a quarter gallon of liquid every 3 days as a supplement and was able to maintain a consistent level of chlorine. This summer I am still replacing the tri-chlor New Water pac every 3 weeks, but losing my chlorine count nearly every day. So, I am supplementing with a lot more liquid and di-chlor granular. Comparatively, several years ago my New Water pacs lasted 4-6 weeks (I could set the guage much lower) and I rarely added granular or liquid (only to shock).

Neal
 

Richard320

LifeTime Supporter
TFP Expert
Jan 6, 2010
20,322
1
San Dimas, CA (LA County)
#4
High CYA doesn't create higher chlorine usage, only a higher minimum level. It should actually decrease consumption.

That being said...high CYA and "normal" FC will lead to algae gaining a toehold, and then you'll see consumption start climbing.
 

imwarren

Well-known member
Jul 9, 2010
88
0
#5
Your chlorine usage is do to something organic consumming it

Your cya could be higher then 110 as the test only is accurate up to 110. You can try a diluted test of 50% tap water 50% pool water then double the result to semi confirm how high it is

With your CC and high chlorine use you are correct to start the shock process the key to the best and fastest results are to measure and dose your fc at least ever hour. After a day or so you will see that it starts to hold longer so you can back off just make sure to test as often as possible. You won't need to test cc every time just make sure you test it near the end of the process

Shock is complete when you pass these 3 points
1 pass overnight chlorine loss test
2 cc less then 1
3 water is clear
 

Neal

Active member
Jul 12, 2012
28
0
SW Michigan
#6
This morning I have passed the 3 criteria shock test. I also brushed the entire pool and cleaned the filter during the process. Due to my high cya level (110) I needed a high FC count. At what FC ppm will it now be safe to let the grandkids, or me for that matter, to swim?
 

BoDarville

LifeTime Supporter
TFP Expert
Jun 5, 2012
3,843
2
DFW, Texas
#8
Neal:

Per the Pool Calculator, at a CYA of 110 you need to maintain an FC level of between 8 and 14 for an ongoing maintenance level.

Jason beat me to it on this next point, but since I had it typed up: From a safety perspective, you can safely swim with an FC level that is somewhere between the above range and just below shock levels (shock level for this CYA is an FC of 26 per Pool Calculator)
 

Neal

Active member
Jul 12, 2012
28
0
SW Michigan
#9
Thanks. I don't know if you read my previous posts in this thread, but I indeed know that I need to drain off some water to lower my cya. In fact, it is likely a substantial amount of water per the calculator. I am planning to wait until September (end of swimming season in Michigan) to do a drain refill. This should put my cya in good shape for next spring when we open the pool.

Neal