Chlorine Block

[verun]

Hello,
So first let me begin by telling you about my pool and its problems. It is an 18,240 gallon in ground pool with a DE filter and vinyl liner. Some things came up in my life last year and I quite stupidly did not cover my pool for the winter. This season the pool was extremely green and after getting the filter running I balanced the chemicals with the advice of the pool store. Currently my readings are FC=0, pH=7.0, TA=120, CA=90, CYA=27. So I proceeded to shock it with 70% chlorine pool store calcium-hypochorite shock from Leslies. Well, I put two bags in last night and I brought the pool water in for testing once again and the pool guy said that the reason the chlorine was not showing up was that there was chlorine block or lock and I had to "burn out" the pool by adding 5 bags of 70% calcium-hypochorite. Should I do this or is the pool guy just trying to get my money (I already have the shock)? I know I should buy my own test kit but for now should I just "burn out" the pool? I should be using bleach and I have bought numerous jugs but should I wait to use that when I am maintaining the pool chlorine levels?

Please Help,
Thanks

 

[Brad S]

There's really no such thing as chlorine block.
You dont have any FC because you have algea. You need to add more chlorine to raise the level high enough to start killing the algea and then hold the chlorine there until its gone. Plain old bleach will work fine. You could buy some 12.5% liquid chlorine, only difference is you will use fewer gallons getting to shock level. Someone will be by shortly to get you going better than i can. In the mean ttime, read this:

pool-school/shocking_your_pool

According to your pool size and pool store numbers, which may be off, you need to add about 6 gallons of 6% bleach to get to shock levels for you CYA level (19 ppm if its mustard algea, even ifd its not, 19 ppm wont hurt). pH is way too low, but this might help the chlorine work. I'd get it up to 7.2 or so at least. The algea is the main concern now.

 

[dmanb2b]

Is CA the calcium reading? Also is your pool plaster or vinyl lined. Either way the burn-out won't harm anything, but your cheaper alternative is bleach, just not most convenient.

His line about "chlorine block" is a line of garbage...CYA is the only thing that blocks FC effectiveness at high levels, but your CYA is not that high. If you choose using the burnout just don;t do it for long periods....we prefer using bleach or you can get liquid shock/chlorine 12.5% from the pool store...it's nice to know you are just using sodium hypochlorite and not other chems...the rest can be adjusted on by one.

Also you may want to raise your PH a tad to 7.2.

 

[verun]

Yeah, CA is the calcium reading. It is a vinyl liner. I already own the shock and I don't think they would let me return in anyhow. Should I raise the pH before doing anything with the chlorine?

 

[Brad S]

I'd start shocking first and get that going. Worry about the other after you get some FC in. As high as your going to raise the FC level, your pH readings to try and adjust it now wont be accurate. You need to raise the FC to ~20 and hold it there. if it falls, which it will, add more bleach to get it back to 20. Once the FC holds overnight, the algea is dead, not before. It may take a few days.

 

[verun]

Would it be detrimental to to use the calcium-hypochorite instead of the bleach and if so should I add the five bags to the pool all at once?

 

[Brad S]

You want to add about 4-5 pounds to get to ~20 ppm from 0 ppm for your pool size. How many pounds in each bag?

Mix it with some pool water in a bucket 1st to mak a slurry, then add it.

 

[MikeInTN]

I'd do any adjusting to the pH now, before shocking. Otherwise you'll have to wait until the FC drops back down to normal before you can get an accurate measurement again.

 

[dmanb2b]

also try to distribute the slurry evenly around the pool...after you add the slurry you may want to occasionaly brush the pool bottom...one of the other reasons we prefer liquid chlorine is it has less of a tendancy to sit at the bottom of the liner like granules can. If you dump all that shock in one spot and sits on your liner it can damage the line

I'm with mike on the PH...you only need a slight adjustment up to 7.2-7.4 at this point...if you start adding bleach later in large quantities, it has a tendency to raise PH as it is basic...bleach PH is somewhere around 11-12 on the PH scale

 

[Brad S]

The pH of that Cal-hypo is almost 12. That might raise it enough to not have to add any soda ash.

 

[dmanb2b]

nice catch Brad...for some reason I was thinking the OP was using di-chlor

 

[Butterfly]

The pH of that Cal-hypo is almost 12. That might raise it enough to not have to add any soda ash.

If OP needs to raise pH, it would be better to use Borax. It has minimal effect of the TA which is already on the high side.

 

[Brad S]

Understand completely. My point was, and is, that if she adds 5 bags of the cal hypo she has now, she might not need to add Borax or anything else at this point. The Cal-hypo may bring it up to 7.2. Besides, she doesnt want to raise it too much since the chlorine will work better at 7.2 anyway.

Add borax, fine (part of the BBB , huh), i just dont think she needs to do anything with the pH until she adds the cal-hypo.

 

[JasonLion]

My point was, and is, that if she adds 5 bags of the cal hypo she has now, she might not need to add Borax or anything else at this point. The Cal-hypo may bring it up to 7.2. Besides, she doesnt want to raise it too much since the chlorine will work better at 7.2 anyway.

Both points are wrong. Once there is CYA in the water, chlorine is just as effective at any PH in the normal range (7.2 to 7.8). And cal-hypo, just like bleach, is PH neutral in the long run. The PH goes up when you add it, and then it goes down again as the chlorine gets used up. The PH still needs to be adjusted regardless of cal-hypo use.

I would first raise the PH to around 7.4 with either borax or soda ash. Then shock the pool. Shocking the pool requires raising the FC level up to shock level as many times as required until the FC level remains stable overnight. 3 lbs of cal-hypo is a reasonable place to start, but don't assume that that will take care of things. It may take quite a bit more chlorine than that, or it might not.

Long term you won't want to keep using cal-hypo. For now your CH level appears to be reasonably low (if CA is calcium). But cal-hypo will increase the CH level every time it is used and eventually get it too high.

 

[Brad S]

I guess we can disagree, then.

 

[chem geek]

"People, I just want to say, you know, can we all get along?" I don't think this is a big deal either way since the pH is starting out at 7.0 and isn't at a dangerously low pH. Shocking will raise the pH and as noted when the FC is allowed to drop when the shocking is done the pH will drop back down. It might not get all the way back to 7.0, but might be close. So pH could be adjusted at that time.

At the 27 ppm CYA (which sounds like a pool store measurement I wouldn't trust) the shock level of around 12 ppm FC would raise a pH of 7.4 to around 7.9 resulting in 0.30 ppm "active" chlorine while starting at 7.0 the pH would rise to around 7.2 with an "active" chlorine of around 0.41. Either way, the algae is going to get killed and the pool cleared -- the latter situation leaving the pH lower to start with might be a little faster, but it's not a big deal either way and you could easily compensate for this with a different FC shock level. As was noted, the effect of pH on "active" chlorine (hypochlorous acid) levels is not as strong when CYA is present (a comparison of traditional industry graphs of this with the "true" graphs when CYA is present is shown here).

Richard

 

[frustratedpoolmom]

Off Topic remarks have been removed. Please refrain from these type of comments as they violate forum rules. Moderator.

 

[verun]

Hi again,
So I put the 5 one pound bags of 70% Cal-hypo in the water and allowed the pump to run for around 4-5 hours this afternoon. After that time I took the pool water to the pool store and had it tested for FC. They claim that the level was 3 PPM! Could this be possible if I put 5 bags of shock in. What should I go about doing now?

Thanks

 

[reebok]

if you have a lot of organics it's possible. this is why the #1 recommendation here is to get your own good test kit. that way you can know for sure and not be a slave to errant testing.

 

[dmanb2b]

it's possible, although pool store do sometimes have inaccurate readings. Chance are you Chlorine is getting eaten up by organics/algae.

My advice, head to your local walmart and stock up on 10-15 182oz bottles of their non-scented Great Value Bleach...you need to get your water back up to shock level asap and keep it there as described in pool school, in the how to shock your pool.

Also...what was your PH? You may want to adjust it now since the FC is low again. Please post the full results they gave you