Really High Chlorine Demand

[msjohnson2868]

Just installed a chlorine generator, and have discovered that my pool has a HUGE chlorine demand problem. Honestly, I haven't been that diligent in measuring the demand before, just added Chlorine tabs to the feeder to keep the pool from getting green. Was constantly adding it, shocking, etc....just thought that was how it was. But now, since installing the SWG two weeks ago, I've been looking closely at the chemistry, and discovered this huge demand. Here's the breakdown of the chemistry, pool details are in my sig:

Salt: 3100 ppm
Free cl: 0.0
Total cl: 0.2
Total Alkilinity: 68
pH: 7.2
CH: 72
CYA: 53
No copper/iron
no TDS
Water Temp 87f

I have recently done a partial drain because the CYA was off the charts, I believe it was at about 150-200 because I drained off 66% of the volume and now it's 53. This was from the constant addition of stabilized tablets/shock before the SWG was installed.

Since the SWG, I have not been able to measure any chlorine via test strips, confirmed by pool store testing. But the water is crystal clear, and the SWG is producing as it should (clear cell, can see the cl fog). Here's what I know about the demand:

Last night, raised the free chlorine to 20ppm with Calcium Hypo. Tested with strips to 10ppm by half dilution so I could read the level, then doubled the amount (ended up being a total of 73 oz of 78% Calcium Hypochlorite). This morning (8 hours later), I measured 1ppm Total Chlorine, and 0ppm Free Chlorine.

I have no visible algae, no cloudiness. The only anomaly I notice is a small amount of dark dust-like substance on the bottom. This was worse before the partial drain, so that may be left over fallout of whatever it was (I vacuumed on waste what was there before installing the SWG two weeks ago).

I'm at my wit's end here... Any help is appreciated!

 

[Butterfly]

Welcome to the forum

You have something eating your chlorine. The SWG is producing just enough chlorine to keep the pool from going pond on you. The stuff on the bottom is probably dead or half/dead algae.

Just so you know, even tho your water is clear, you have CC and no chlorine so it is not safe to swim.

Two things you need: A good test kit and read Pool School!

The fav test kit around here is the TF100. Do yourself a favor and order one now. Link in my sig.
You also need salt test if you don't already have one.

In Pool School, you will learn that you need to shock your pool. It is a process and not a one-time event.

You should use bleach/liquid chlorine to shock your pool. A SWG cannot shock a pool because it cannot add enough chlorine at one time to reach shock level.

We can help you take control of your pool. Post back in this thread with any questions.
Someone will be around to help

 

[msjohnson2868]

Thanks for the quick response! Looking at Pool School, it seems that I need to raise the FC to 24 repeatedly until the overnight loss is less than 1ppm,. correct? Just want to be sure before I dump that much cl in there.

 

[Butterfly]

Thanks for the quick response! Looking at Pool School, it seems that I need to raise the FC to 24 repeatedly until the overnight loss is less than 1ppm,. correct? Just want to be sure before I dump that much cl in there.

Well, yes.......you raise to shock level based on CYA and maintain the shock level until the water passes the three criteria that prove you are done shocking. The 3 criteria are listed in my sig in RED; but, do you have an FAS/DPD test kit? That is the only way to accurately test FC that high.

 

[Bama Rambler]

Add enough to get to 24 and test and add every hour. With your test kit you'll have to dilute to test and that'll introduce some error but it's better than nothing.

I know it seems like we harp on a good test kit but it makes your life so much easier knowing what your numbers are and being able to test when you want to. Besides, you'll need the FAS-DPD kit to know when you've passed the OCLT.

 

[msjohnson2868]

Will do...don't have the test kit, only strips for now, but the kit is on the way! Just ordered the Taylor K-2006. Diluting works for now. Will post back and let you know how it goes. THANKS FOR THE HELP...pool store didn't have a clue.

 

[frogabog]

You also may want to bump your CYA up to 70-80ppm for the SWG. 54ppm CYA is a little low.

Of course, do this AFTER you are done shocking. Raising it now will only mean you'll need a higher shock level and more bleach to shock the pool so stick with 54ppm (so accurate... pool store result, yes?). Maybe use 60ppm CYA in the pool calculator in case their result is low, to be sure you're hitting shock level properly. A little extra chlorine won't hurt at all if it's actually accurate.

 

[msjohnson2868]

OK, after this morning's fc reading of 0 after 8 hours of shocking to 24ppm, I shocked again to 24ppm.

Tested (by strips because my kit won't be here for a few days) by 4x dilution at 8:00pm tonight... free chlorine was 14. So my Chlorine demand for 12 hours is 10 ppm. Still way to much, but definitely an improvement.

Added 364 oz of 6% bleach to target 24ppm again.

I'm on the right track, right? Thanks in advance for the help.


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[duraleigh]

I'm on the right track, right? Thanks in advance for the help.

It sure seems like youhaqve it going the right direction. You'll need the FAS/DPD test in your kit to finish the shock process but what you're doing now looks good.

 

[msjohnson2868]

This morning, after last night's shock to 24, the 8 hour reading was 20ppm. Rechlorinated to 24 at 7am. Tested again at 4pm this afternoon, level was 20. I'm going to raise it again now, and then again when it gets dark for an overnight test.



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[msjohnson2868]

As far as I can tell measuring by dilution with test strips, I maintained a 24ppm overnight! Hopefully my kit will be in today or tomorrow so I can confirm.

One question...if I stop the shock process now, and I'm not quite rid of the CC, is it going to hurt anything? Since the dilution I have to do is 8x to even think about accuracy to 1ppm on the test strips, I don't really trust that I can confirm the <1ppm chlorine loss overnight. It looks to be true, though...a 4x dilution says really close to the same thing.

 

[duraleigh]

if I stop the shock process now, and I'm not quite rid of the CC, is it going to hurt anything?

Generally, we encourage you not to do that. But it is because folks new to BBB simply DO NOT understand the shock process as we teach it and are content with a one-time dose....resulting in failure.

So, if you lower your FC now, and you have residual organics, and you allow them to re-establish in your pool, you will be right back where you started from.

As far as performing the OCLT with strips, I would say it is about the same as doing it with tarot cards. It is a waste of time.

If it were my pool I would keep the FC up at shock value and wait on your kit so you can stop guessing.

 

[msjohnson2868]

Well I didn't have much choice in ending the shocking process. Had some things come up at work and had to let the pool sit for a day.

But all looks good I think. Here's the results...FROM MY NEW TAYLOR K-2006 TEST KIT!

This is a full 36 hours since adding any chlorine.

FC 19ppm
CC 0 (woot woot!)
pH 7.2
CYA 30
CH 140

Here's one question. I realize the pH is low and the test may be affected by the high fc levels. Can the CYA be low for the same reason, or should I go ahead and add some?

I haven't had the SWG on during this whole process and am waiting on the FC to come down a bit before I do.

Your input and wisdom is appreciated. Thanks for helping me get this far.

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[linen]

Time to do an OCLT now that you have the right tool. See: http://www.troublefreepool.com/pool-school/overnight_fc_test
Continue to leave your swg off. Remember you are done with the shocking process only when you meet all three requirements in my sig.

Let us know if you have questions!

 

[msjohnson2868]

Should I address the low CYA now or wait until the fc drops to normal levels?

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[linen]

Should I address the low CYA now or wait until the fc drops to normal levels?

Finish the shocking process first. Did you get to do a OCLT last night, or will that be tonight?

 

[msjohnson2868]

Doing it tonight. I did do a good vacuum on waste and added some water back prior to that last test. So the CYA could have come down some as a result of that.

Will let you guys know about the OCLT tomorrow.


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[msjohnson2868]

Ok the OCLT was good! Only lost 0.4 ppm overnight. FC was 13.8 and CYA was 40.



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[msjohnson2868]

To all you guys who helped me out...thanks a million. The water is now perfect. Swam in it yesterday and for the fire time since I've had it installed, no eye burning, no pungent chlorine smell afterwards. Kudos to all of you!


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[Butterfly]

To all you guys who helped me out...thanks a million. The water is now perfect. Swam in it yesterday and for the fire time since I've had it installed, no eye burning, no pungent chlorine smell afterwards. Kudos to all of you!


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congrats!
Can you post a pic for us? :-D