To shock, or not to shock?

[jrichv]

I am a new pool owner, with a 25,500 gallon in-ground gunite with pebble/plaster finish, using the BBB method with TF100 test kit since the new pool was handed over to me about a month ago. I ditched the pucks as soon as I passed the pool builders pool school and he was pulling out of the driveway.

I have some questions - I'm not in any trouble yet, but I'm looking to head off any problems beforehand. My water is blue, crystal clear, and danged near perfect, IMHO - but after reading topics here, and doing my testing diligently, I got the feeling I was losing too much chlorine during the day and decided to perform an OCLT overnight last night. The pool is in north central Texas, and gets 100% sun all day. Typically I'll test in the evenings when I get home from work, and usually have 0 to 0.5 FC, and usually 0 CC, but occasionally 0.25. Normally not a heavy bather load - just my 2 kids, and sometimes one of their friends during parts of the day.

I was gone all weekend, returning home Sunday evening. FC was 0, and pH was at 7.8 (last treated on Thursday evening), so I added my 212oz of bleach, and 69oz of acid Sunday evening. Monday afternoon, I had 1.5 FC, 0.25 CC, and pH 7.5 = treated with 185oz bleach, and 42oz of acid (I was shooting for an FC level of 5.0 to prep for my OCLT last night)

Here's where it gets interesting - after dark, and after about two hours of running the pump/filter - my FC was at 7.0ppm and pH was at 7.2.

7.0 > 5.0, by a long shot. Either I don't have 25,500 gallons, or I measured wrong?

And for the big payoff: this morning, I got up early to test, and when I went and grabbed my first water sample, I realized the pump/filter wasn't running. So I turn it on, and go make a pot of coffee, coming back 10 minutes later and take my water sample. FC = 5.0, pH 7.2... So now comes the question - 2.0ppm FC drop overnight means I have to shock??? Or, should I have let the water circulate for more than 10 minutes in order to "even out" my water sample?

The full test results for the chem-geeks among us (you know who you are! :-D ):

-------7/8------7/9(5pm)---7/9 (9pm)---7/10 (6am)
FC------0--------1.5---------7.0*----------5.0**
CC------0--------0.25---------0--------------0
TA----110--------110
CH----230--------240
CYA----40---------40
pH-----7.8--------7.5--------7.2-----------7.2

* What the....???
** <expletive deleted>

Thoughts and suggestions requested please? And thanks in advance!

 

[Richard320]

Since you've let FC run down to zero, and you're losing FC in the dark, I'd perform the shock process.

And I suggest you purchase a wall whale brush. You can move and mix some water with that, there will never be a question if it's well mixed if you make a few passes with a wall whale first.

 

[jrichv]

Since you've let FC run down to zero, and you're losing FC in the dark, I'd perform the shock process.

And I suggest you purchase a wall whale brush. You can move and mix some water with that, there will never be a question if it's well mixed if you make a few passes with a wall whale first.

Thanks, Richard320 - I will gear up to begin the shock process, and figure out what bait and tackle one needs for landing a whale... :lol:

Any thoughts on why my FC went to 7.0ppm when I was aiming for 5.0ppm?

I am certain I measured correctly - I'm very meticulous when it comes to that sort of stuff.

 

[benavidescj]

You may want to redo the overnight test. Sounds like the water did not mix well enough when you took your reading.

 

[jrichv]

You may want to redo the overnight test. Sounds like the water did not mix well enough when you took your reading.

I re-ran the OCLT test last night/this morning, and I gave the pump/filter a one-hour head start before I took my sample this morning. I lost 1ppm of FC overnight. :-? CC was still at 0.25ppm.

I'm going to run through a shocking sequence starting Friday morning (the ability to work from home rocks!), as I should have my refills for my CYA reagent in the mailbox by then.

Next Question: Let's say that the pool shocking process takes 24 hours, and use a shock FC level of 20ppm as an example. At the end of the process when the FC is no longer dropping and staying steady at 20ppm, how long (on average) will it take for the FC level to drop back down to a reasonable and swimmable level? Say, 5-7ppm FC? The kids are going to be hounding me with "when can we swim, Daddy?" questions as soon as I start the shocking process.

 

[duraleigh]

How are you getting .25ppmCC? You should be using a 10ml sample which will yield increments of .5ppm.

Once your pool is clear (and it will surely take longer than 24 hours....sorry), It'll take a few days For FC to drift down to maintenance level BUT it is safe to swim in the pool at FC levels up to shock value so they can swim immediately upon completion of the process.

 

[jrichv]

How are you getting .25ppmCC? You should be using a 10ml sample which will yield increments of .5ppm.

New math? My bad - it's 0.5ppm (1 drop X .5 = 0.5ppm) Math is hard... :lol:

Once your pool is clear (and it will surely take longer than 24 hours....sorry), It'll take a few days For FC to drift down to maintenance level BUT it is safe to swim in the pool at FC levels up to shock value so they can swim immediately upon completion of the process.

Therein lies the rub - the pool is clear now (maybe just a tad cloudy, but not much), I'm just trying to stay ahead of any algae infestation, and trying to figure out why I'm losing so much FC on a daily basis? In my mind, if I shock it and get to a known clear and clean algae-free baseline, then I can look at other solutions?

 

[duraleigh]

My bet is you won't need to look for other issues. Your FC has been too low in the past and you have not added enough to kill the algae (that you can't see) that remains. If you shock properly, I'll bet your issues will be over.

How did your pH drop so fast? Did you put pucks in the pool or did you lower it with MA to prepare to shock?

 

[jrichv]

My bet is you won't need to look for other issues. Your FC has been too low in the past and you have not added enough to kill the algae (that you can't see) that remains. If you shock properly, I'll bet your issues will be over.

How did your pH drop so fast? Did you put pucks in the pool or did you lower it with MA to prepare to shock?

I hope shocking solves my issues - can't wait to get my CYA reagent in the mail so I can get a good CYA reading and get started! And I got a Wall Whale brush yesterday - that thing rocks!

pH droppage? No pucks in my pool... I use MA only. I get my bleach from Sam's Club, and MA from Lowe's.

 

[adeller]

I had similar issues with chemicals giving me larger results than I anticipated. I was using the pool size the builder gave me (12,500 gal). Every time I calcualted the chem additions based on that value with the Pool Calculator (http://www.poolcalculator.com/), I would get more reaction than anticipated. After tinkering with the number of gallons and measuring the pool and using the estimator at the bottom of the calculator, I get a number more like 9,000 gal. What I did was, after an addition of a known amount of chemical and measuring the reaction, I changed the gal figure until Pool Calc came up with the same calculated result. This proves out when I add chemicals, I now get exactly, or very close to, the reaction that was calculated. I guess you could say I calibrated the pool size in the calculator to match the actual results.

 

[jrichv]

Update - I am neck-deep into shocking, and my pool looks great!!! Crystal clear, and dare I say that I am suffering from sparklypoolitis?

I started last night, and an hour after my initial bleach-bombing chlorine insertion I was reading at 17.5ppm. It went as low as 13.0ppm after dark, and I ran it back up to 14.0ppm around 11:30pm. This morning's first test registered at 12.0ppm (around 10:00am) and my attempt at raising the chlorine back up to 14.0ppm was a little "off" - I overshot it but am back to 14.0ppm as of 3:00pm (just a few minutes ago).

My CYA was not registering at all last night - tube full, black dot still visible - so today I found some of the PB's left over conditioner (100% CYA) and added 32 oz by volume. The pool calculator said 67 oz, but I didn't want to over shoot that by any means. I mixed it in a 5 gal bucket of pool water, but it didn't really dissolve at all - I can still see it very clearly on the bottom of my pool. Hopefully it will dissolve in a couple of days?

 

[Richard320]

...

My CYA was not registering at all last night - tube full, black dot still visible - so today I found some of the PB's left over conditioner (100% CYA) and added 32 oz by volume. The pool calculator said 67 oz, but I didn't want to over shoot that by any means. I mixed it in a 5 gal bucket of pool water, but it didn't really dissolve at all - I can still see it very clearly on the bottom of my pool. Hopefully it will dissolve in a couple of days?

Let's hope it doesn't leave spots on the plaster.

Too bad you didn't read Pool School where it says

CYA - Cyanuric Acid

CYA can be raised with cyanuric acid. Cyanuric acid is sold under a variety of names, including Stabilizer, Conditioner, Instant Pool Water Conditioner, Stabilizer 100, Stabilizer & Conditioner, etc. Instant Pool Water Conditioner is a liquid product which is significantly more expensive than the other forms.

Solid cyanuric acid should be placed in a sock, and the sock put in the skimmer basket. After adding solid cyanuric acid you should leave the pump running for 24 hours and not backwash/clean the filter for a week. Solid cyanuric acid can take up to a week to fully register on the test, so it is best not to test the CYA level until one week after adding some.

 

[jrichv]

Let's hope it doesn't leave spots on the plaster.

Too bad you didn't read Pool School where it says

CYA - Cyanuric Acid

CYA can be raised with cyanuric acid. Cyanuric acid is sold under a variety of names, including Stabilizer, Conditioner, Instant Pool Water Conditioner, Stabilizer 100, Stabilizer & Conditioner, etc. Instant Pool Water Conditioner is a liquid product which is significantly more expensive than the other forms.

Solid cyanuric acid should be placed in a sock, and the sock put in the skimmer basket. After adding solid cyanuric acid you should leave the pump running for 24 hours and not backwash/clean the filter for a week. Solid cyanuric acid can take up to a week to fully register on the test, so it is best not to test the CYA level until one week after adding some.

I read that and shot outside like a flash! I had moved the CYA around a couple of times since adding it - using my old brush head - and just now when I swept it again to move it, it disintegrated. The plaster appears to have been spared!

Ok, now back to Pool School - I have read it several times, and remembered reading the sock-in-the-skimmer technique for adding CYA - but I guess I just forgot about it? I was chatting with a fellow pool owner this morning, and he mentioned his way of mixing it in a 5 gal bucket with pool water - maybe that is where I got off track?

Who knows? But it appears the crisis has been averted. Thanks for keeping me on my toes!

 

[jrichv]

Another Update: at 5:30pm I have 14.0ppm FC - same as I had a 2:30pm (wooHoo!); and, for the first time my CC is 0!

One side effect of crystal clear water: when you run the brush on the bottom of the deep end, you can see how much dirt/dust/dead organics is really in your pool... Time to vacuum.