Chlorine went down to 0 - must I shock?

[Aubade]

Hi All. I'm a new inground fiberglass salt water pool owner - just got it last summer. So far using advice from this site has been working great! But last week I went on vacation, and there must have been a power outage in a storm that popped the breaker panel outside and caused everything to stop working on the timer we set.

I don't know how long it was like that. The water itself still looks clear. I tested immediately (I have the Taylor FAS-DPD kit) and the water didn't even turn red from the powder so the chlorine level was 0. I started the filter and SWG back up and have been running it overnight, now it is up to 1.5 ppm. I'm out of liquid chlorine (I put extra in before I left for vacation) otherwise I'd put that in. I'm going to stop after work to get some more.

But my question is - as long as the water looks OK, and I get it back up to 4 ppm where I usually keep it, is it safe to swim? Or do I need to shock it and wait a day or two before we swim in it again? It is going to be nice this afternoon, so I'm sure my son will want to go in!

 

[sccm_sysadmin]

SLAM it.

If you had it good to go before the vacation it will likely be a quick SLAM. Better safe than sorry, especially if you have small children.

 

[mknauss]

Welcome to the forum! Glad you have had success with this pool water management method.

Your best bet is to do an OCLT tonight. You should get your FC to 10 (You did not say what your CYA is but I assume 70?) this evening. Test after the sun is off the pool completely. Run your pump overnight but TURN OFF your SWCG. In the morning, before the sun shines on the pool, test the FC. If your FC loss is 1 ppm or less, you are good. Keep your FC at the high end of your range for a few days and see how it goes. If you have a greater loss of FC, SLAM. It should go quick, but hit it hard and keep the FC at shock with very frequent test/dose of bleach.

Take care.

A couple more items. An FC of 4 is pretty low. With my CYA at 70 I keep my FC at 7. You are far better keeping your target at 10% of CYA. You can go lower, but any increase in bather load or other organic additions can put you at risk.

Also, you can safely swim in the pool with FC up to shock level.

 

[Aubade]

OK, I will do the OCLT tonight, that makes sense.

Last I checked my CYA was 70. I should do a full testing again tonight.

i had been keeping it at 6 or 7 earlier this summer, then I read something about that being too high (cant remember why now) so I put it down to 4. I will keep it higher again to 7 after this just to be safe.

thanks for the quick replies!!

 

[Aubade]

OK I did a full test tonight. Here's what I got (though it was after dark so not in perfect light)


FC - 6
CC or TC - 0
pH - 8.0
TA - 105
CH - 105
CYA - 65-70ish


[FONT=arial, sans-serif]I put in about 45 oz 12.5% liquid bleach to raise it to 10, and turned off the SWCG (but left on the filter). Just tested again and it is right about 10. Here's hoping for the morning reading being no less than 9!

I guess I also need to do something about the high pH and low CH though, if it is going to be perfect. Any advice welcome!


[/FONT]

 

[mknauss]

You do need to add muriatic acid to lower your pH. Target 7.2 and use PoolMath for amount.

The CH does not matter much as you have a fiberglass pool. Do you have a grouted water line tile?

Take care.

 

[Aubade]

No, no grouted water tile line, just fiberglass to concrete.

It went down to 8. Darn. Guess I have to SLAM it.

 

[Aubade]

I'll just keep posting my updates here in case it helps anyone else.

My husband used PoolMath to add some muriatic acid at lunchtime (he works from home unlike me) and successfully lowered the pH to 7.4 with one dose.

I did another full test when I got home from work. I downloaded the new Pool Math app and have to say I like it so far! Way easier than me typing everything into an email or iPhone Notes like I was doing before.

Readings at 7:33pm were:
3.5 FC
7.4 pH
110 TA
105 CH

Then I added nearly 2 128 oz jugs of 12.5% liquid chlorine to get it to 26 FC.

Will test it again tomorrow and do an OCLT tomorrow night.

 

[Aubade]

OK so this morning the FC was down to 16 at 9:42am.
I added a bit too much liquid chlorine (oops) and put it back up to 30.5 at 9:59.
Now at 1:15pm it is down to 21.5, but 0 CC.

Do I really need to keep raising the FC to 28 even though it is 0 CC and the water is sparkling clear? This seems excessive.

 

[mknauss]

Once you can run the OCLT and confirm you have no more organics you can call it complete.

It is your pool. If you wish to stop - it is your decision. If the algae returns, you know how to SLAM. But we recommend finishing to the end.

Take care.

 

[Aubade]

What sort of organics might be in there? They must be microscopic if the water is clear. I have no doubt it is possible - just curious what it could be if you can't actually see any algae, and there were no people in the pool since we left on vacation.

Here is a pic of my pool, just took it 5 min ago:

 

[Aubade]

just tested again. 16 FC. i can't understand how it would go down so much when the pool looks clean!

 

[Philo]

If you had a microscope, you'd be shocked (no pun intended....)

 

[turbowop]

I went through the same thing. Started with a perfectly clear pool that couldn't hold chlorine. 60gallons and a couple weeks later I was finally able to hold chlorine overnight. Read my thread if it makes you feel better:

New pool owner and first test results from my test kit

 

[jstephens1]

You should do the cya test during the day with the sun to your back. I noticed you said it was 70 but it was after dark.

 

[Aubade]

i wish i had a microscope! i want to know what's in there.

in any case we put more chlorine in. my husband put a bit too much, went up to 30.

i will test cya in the sun tomorrow.

i really hope this doesn't take a week!! i want to swim.

 

[mknauss]

i want to swim.

Then swim! As long as your FC is below your shock level based on CYA. Don't wear your designer swim suit but it will be harmless. You will never know the difference.

Take care.

 

[JimMarshall]

Then swim! As long as your FC is below your shock level based on CYA. Don't wear your designer swim suit but it will be harmless. You will never know the difference.

Take care.

Designer swimsuit should even be fine. At 30 PPm you're talking half a cup of 8.25 diluted in a gallon of water.

 

[setsailsoon]

I read through this post and don't see you ever got an answer to the question about where are the organics and how could they be there if my pool water is so clean? Your pool is a very dynamic system with materials continually added and taken out by natural means and your equipment/treatment chemicals. With the chlorine disinfection method used by TFP you are protected by a level of FC such that any threats like disease causing bacteria or undesirable stuff like algae are immediately reacted by the "reserve" of FC you maintain. Organics can be solid material such as algae, dirt, other debris that cloud the water or change color or even dead things in your skimmer like a frog or something. They can also be chemicals such that are completely soluble in water such as organic acids and waste products like urine and even the intermediate components created when chlorine reacts with matter in your pool to protect you. You can't see most of the soluble compounds. They are like sugar in water; even though you can't see them they are definitely there. They all react with chlorine that is consumed in the continuous reactions that happen in your pool. The reactions go through several steps and eventually the undesirable chemicals are converted to gases and vaporize from your pool or solids and they get removed in the filter. If you don't complete the SLAM process they will continue to consume chlorine until they are gone and this can allow your pool FC level to drop so you will have an algae bloom or some other undesirable result... not fun!

So hang in there and get rid of whatever is consuming your FC at night.

Incidentally, I travel monthly so I run with my CYA at the low end of TFP's recommended range and I use trichlor tablets if I'm going to be gone more than a couple of days. I use liquid bleach at all other times so my trichlor additions are just enough that I don't have the buildup of CYA. Trichlor does degrade but very slowly and if used as the main source of FC it will result in CYA levels waaaay too high. Been working fine this way for two years. One time I was even gone for 2 weeks! Another tip I got early on was to record my test results and actions taken. Every pool is a little different and this helps you get to know how your pool reacts to different situations.

Good luck to you and I hope this helps!

Chris

 

[Aubade]

My son will be happy he can swim! He was going to have to resort to the slip and slide today.

Thanks Chris! That is interesting and good to know.

Last night it went to 23 (from 30).

Also just want to make sure I'm doing this right - I have to keep bringing it back up to 28 until it stays there overnight, right? (even if CC is 0) Or do I let it go down to 10 since CC is 0 then do the OCLT?