Chlorine at Zero - please help.

[Dimes]

Can't seem to get any chlorine to stay in my pool. Have 7 3-inch tabs in the chlorinator and added 3lbs of shock last night, but still reading zero when tested at Leslies and via my own home test. Leslies says it is the infamous "Chlorine Lock" and to just keep dumping in more Shock until Chlorine rises. Is this what I should do? I have this greenish dust that has been coating a good amount of my pool floor and walls of late - so maybe the chlorine is being used up attacking that? I even added conditioner 2 weeks back based on Leslies recommendation as they thought that might be why I was losing chlorine.

Here's my most recent readings:

FAC: 0
TAC: 0
CH: 230
CYA: 40
TA: 90
pH: 7.6

Thanks!

 

[pooldv]

How/where did you get that CYA number? It sounds to me like your CYA could be much higher. It sounds like you have algae growing and consuming your chlorine and need to Pool School - SLAM - Shock Level And Maintain the pool. But, I want to validate that CYA number first.

 

[poolnoob.ca]

I agree with pooldv, if youve had pucks in the skimmer all year and dumping in the shock the cya must be way more than 40. I foresee some draining and refill to lower cya and a TFP-style SLAM

 

[Patrick_B]

Welcome Dimes,

Does your kit have a Cya test? This one is often the worst one from stores, but let us know, and we can help. Whatever is going on, we can help you fix it no worries. We can also show you how to gain control of it and never play a guessing game again, or have to lean on the pool store for help.

You don't have Chlorine lock, and it's the Algae using up the Chlorine. Easily overcome I promise.

 

[tim5055]

I agree with the other folks here, your CYA is probably much higher unless you have regularly replied large quantities of pool water. With your higher than normal CH either you are in a high CH area like Arizona or have been using CalHypo shock.

Stop listening to Leslie's as their advice is geared to chemical sales as the primary goal. Switch to liquid chloerine products only and get your own quality test kit so we can see what that CYA really is.

Please add your location to your profile as it helps us in our advice.

 

[Dimes]

Thanks all.

Can you recommend a CYA test kit?

When you say switch to "liquid chlorine" - do you mean stop using both the chlorine tabs for the chlorinator and the powder shock, or just the shock?

And what would I switch to?

Thanks everyone for the suggestions.

 

[sbcpool]

Liquid chlorine means no tabs and no powders. Only liquid chlorine. Also, don't listen to your pool store. Often they're much more interested in finding the best way to sell you a lot of stuff, or at least don't really understand the underlying chemistry.

 

[Dimes]

I just ordered the Tf-100 Kit - so will be bale to calculate CYA myself soon.

Assuming my CYA is indded higher than Leslie's is telling me - is there a way for me to calculate how many gallon jugs of bleach to add to my pool (29k gals) to get the FC back to where it needs to be?

 

[Patrick_B]

I just ordered the Tf-100 Kit - so will be bale to calculate CYA myself soon.

Assuming my CYA is indded higher than Leslie's is telling me - is there a way for me to calculate how many gallon jugs of bleach to add to my pool (29k gals) to get the FC back to where it needs to be?

Sure there is, and it's easy. You can use the Cya/Chlorine chart in Pool School, and use Pool Math to calculate your dose. That said, you'll want to drain and replace water to lower Cya before you start a SLAM if it is high after you test. Congrats on taking the right step!

 

[sbcpool]

I just ordered the Tf-100 Kit - so will be bale to calculate CYA myself soon.

Assuming my CYA is indded higher than Leslie's is telling me - is there a way for me to calculate how many gallon jugs of bleach to add to my pool (29k gals) to get the FC back to where it needs to be?

It varies a lot depending on the CYA levels. If it were me I would add enough liquid chlorine to get the free chlorine up around 10 or 12. That's high enough for a fairly high CYA and not crazy high if your CYA really is around 40. If your current free chlorine really is 0 and your pool really is ~30,000 gallons, it will take two or three gallons of bleach to get there. Perform an OCLT to see if you have a need to SLAM your pool.

Keep in mind that you cannot successfully SLAM without an FAS-DPD chlorine test kit. What type is your current test kit?

 

[Dimes]

It varies a lot depending on the CYA levels. If it were me I would add enough liquid chlorine to get the free chlorine up around 10 or 12. That's high enough for a fairly high CYA and not crazy high if your CYA really is around 40. If your current free chlorine really is 0 and your pool really is ~30,000 gallons, it will take two or three gallons of bleach to get there. Perform an OCLT to see if you have a need to SLAM your pool.

Keep in mind that you cannot successfully SLAM without an FAS-DPD chlorine test kit. What type is your current test kit?

Current kit is just the basic FC and ph kit. Then I also have some strips as well that supposedly measure other things.

 

[sbcpool]

Current kit is just the basic FC and ph kit. Then I also have some strips as well that supposedly measure other things.

The problem with those kits is that they can't measure FC above 10 ppm. If your CYA is over 100 you can't even tell if you have enough FC with one of those test kits, and a SLAM is impossible.

 

[poolnoob.ca]

Hi Dimes, great job ordering the TF-100, please post us up some results when you get it. Here are videos of how to do each test while you are waiting: https://www.youtube.com/user/TF100TestKit/videos

 

[Dimes]

Just got my kit....my CYA is at 100...FC is at zero. Pool store had my CYA at 40...what a joke!
So what's next steps from here?

Thanks again!

 

[tim5055]

Well, 100 is the limit of the test, so it may be 100 or some number much higher. The only way to reduce CYA is to drain water and replace it. With a vinyl pool you never want to go lower than 1 foot of water covering the shallow end.

To get rid of the green you will need to SLAM, but you really can't do it at those CYA levels.

 

[pooldv]

Try the diluted CYA test and see what you get.

More in post 8 here, Extended Test Kit Directions

 

[Dimes]

Try the diluted CYA test and see what you get.

More in post 8 here, Extended Test Kit Directions

Looks like my CYA has come off a bit. Added about an inch of fresh water from hose last night and looks like with the CYA test and diluted test I'm coming in between 80 and 85 or so. Adding more fresh water tonight and will retest.

Should I hold off on adding the liquid chlorine until I can get it much lower?

 

[chem geek]

You should have chlorine in the water even while working on lowering the CYA. The chlorine will help prevent algae growth and it's a lot easier to prevent than it is to clean up an algae bloom. Some pools operate at 80 ppm CYA -- most SWG pools and some pools in very hot sunny areas. You can continue your dilution over time, but I'd get chlorine in there now.

 

[pooldv]

Have a look at this, Pool School - ABCs of Pool Water Chemistry. Chlorine needs to be maintained at target level for your CYA at all times, Chlorine CYA Chart

and here is the process to Pool School - SLAM - Shock Level And Maintain your pool when you get ready.

You can SLAM your pool with 80 CYA. I had to SLAM mine with 70 cya a month ago because I let my FC drop to 1.5ppm a little too long. Or you can lower it closer to 40 or 50 and then SLAM. Your climate doesn't need 80 CYA.

 

[gwegan]

I'd drain some water at least a foot and then test for CYA after filing back up. Keep adding some chlorine to the pool so the algae does not go crazy. SLAM with a CYA of 80 is not cheap with 26,000 gallons. Try to get your CYA to 40.
OrThe CYA test is not easy-- but you can use the same solution and do the test a few times. Or have your spouse do it and compare your results.