Chlorine keeps going back to 0

Paultex6223

Member
Jun 12, 2015
9
Round rock texas
Hey everyone! So my pool is finally up and running and we have had it for about 1.5 months now. It is around 18k gallons pool and spa. No salt system.

I am having major issues keeping the chlorine where it needs to be.

Here are my current readings

PH - 8.2 (It's been around 7.8 for a while, but went up a little over the last few days)
Chlorine - 0
Alkalinity - 90
CYA - 30

I used tablets in the start, my builder recommended them through the feeder, however after reading on here about them, I figured I would use just a bit to get the CYA numbers up. I now have been using liquid chlorine and I just cannot seem to keep the number off 0. We did half a gallon 2 days ago and measured yesterday, back at 0. Did another half gallon, measured today, back at 0.

Any recomendations?

Also I have the TF-100 kit.

Thanks,
 

Brett S

Well-known member
Mar 15, 2019
703
Orlando
So half a gallon of 10% bleach will raise the chlorine level in an 18,000 gallon pool by only 2.8. Your pool is almost certainly using more than 2.8ppm of chlorine in a day. You need to be adding more chlorine than that.

However, even besides that, since your chlorine level has gotten so low it’s very likely that there is algae in your water now, which will also consume chlorine very quickly. So you will probably need to do a SLAM to make sure there is no algae left and then add enough chlorine to make sure that you never go below the minimum level for your CYA level.
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,180
Central California
When referring to the FC/CYA chart, you'll see a column for "Minimum FC" and another for "Target FC." For your CYA of 30, minimum is 2 and target is 4-6. I ignore Minimum FC and use the low end of Target FC as my minimum. So in your pool, I'd try to never let the FC fall below 4 and I'd try to keep it always at 6. That way, should you get a little lazy, or have a bunch of kids in the pool doing "there thing," or maybe have a very hot day or a bunch of birds bomb your pool, whatever, you have this built-in reserve of FC to cover those situations. Don't run your pool down to the minimum if you can help it, because you then won't have any wiggle room, and an algae outbreak can happen very fast.

Test often while you learn your pool, and how much chlorine it wants. After a while you'll be able to dose more often than you test, because you'll find your pool uses about the same amount everyday. If you know you're going to have a party, you might up that day's dose to cover the extra swimmer load (people in a pool can use a lot of chlorine (sweat, suntan lotion, and "that other stuff")). Then you test the FC after they're gone and "top off" the chlorine they used up. Next day you go back to your regular dosing. You'll get it.
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,180
Central California
By the way, this is why we all have saltwater pools and use SWGs, which maintain the right amount of FC everyday, without us doing much of anything, including lugging chlorine from the store every week. They're better for you and your pool. If you tire of dealing with liquid chlorine, you might end up with an SWG yourself.

By the way, congrats on figuring out the bad advice your PB gave you. Tabs don't work long term. You gotta do liquid often or convert to SWG. And for using the test kit. You are way ahead of the learning curve for a new pool owner.
 

BowserB

Silver Supporter
Jul 29, 2018
334
Katy, Texas
Paul, we don't "all have saltwater pools." I use 12.5% liquid chlorine with CYA maintained at 40. I've found that I lose a lot of chlorine in the sun at 30 CYA. You can get your CYA up using the tabs as your chlorine source (although you might want to hit it with a gallon of liquid chlorine up front.) Use the tabs until your CYA hits 40. Then maintain chlorine at around 5ppm with liquid chlorine, and you'll be OK. When my CYA gets low--and it does sometimes in the spring and under the Texas sun--I put tabs in a floater until CYA is back to 40. I could go as high as 50 CYA without needing really high chlorine, but I keep it at 40 in case we need to be away for a few days and use tabs while we're gone.

The overnight chlorine loss test (OCLT) will tell you if algae is consuming your chlorine. First get the chlorine up to an easily measurable level--like 5 or 6 ppm. Check the chlorine after the sun is off your pool. Check again the next morning before the sun hits the pool. If you've lost more than .5 ppm chlorine, you may have an algae problem.
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,180
Central California
Bill, I shouldn't have made such a general statement, of course many pool owners don't have SWGs. In my head I was referring to all of us TFP admins, mods, experts and guides. Admittedly I don't have the exact numbers on that, but I think you'll find that most of "us" do. What I should have said was: all of us that now use SWGs would not likely ever revert to a non-SWG pool. How's that? ;) Until you've used one, you don't know what you're missing!
 

Paultex6223

Member
Jun 12, 2015
9
Round rock texas
Sorry if this is obvious, but are you aware that your pool loses chlorine every day? You need to add chlorine continuously to keep the level up.
Yes, I know it loses chlorine daily. There’s either been tabs, or I’ve added chlorine pretty much daily, or sometimes every other day.

I’ve been worried to add too much chlorine in a fresh plaster pool. Should I be good at this point, as it’s been about 1.5 months I think.

also, how much do you think I should add today?
Thanks guys,
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,180
Central California
If there is any actual concern about chlorine on new plaster, it'd be the first couple of days. You're good to go! An algae outbreak on new plaster is the bigger concern, because then have to blast the pool at SLAM level. Better to never get algae than to be shy with the chlorine.
 

Paultex6223

Member
Jun 12, 2015
9
Round rock texas
If there is any actual concern about chlorine on new plaster, it'd be the first couple of days. You're good to go! An algae outbreak on new plaster is the bigger concern, because then have to blast the pool at SLAM level. Better to never get algae than to be shy with the chlorine.
Cool. I’ll get out there tonight when I get home and get some added!
 

PoolNewb2020

Well-known member
May 7, 2020
297
Lathrop, CA
Are you using the Pool Math app? If not I would highly recommend it. It will tell you exactly how much to add to reach a certain ppm level for all chemicals needed, not just chlorine.

Half a gallon every two days on an 18k gallon pool is certainly not enough. Liquid chlorine needs to be added daily and with a new pool tested daily as well to get a feel for normal FC loss.
 

Dtkokay

Well-known member
Dec 31, 2019
305
Houston, Texas
Yes, I know it loses chlorine daily. There’s either been tabs, or I’ve added chlorine pretty much daily, or sometimes every other day.

I’ve been worried to add too much chlorine in a fresh plaster pool. Should I be good at this point, as it’s been about 1.5 months I think.

also, how much do you think I should add today?
Thanks guys,
Gotcha! With chlorine, too much is better than too little.
 
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Katodude

Silver Supporter
Aug 22, 2017
1,065
West Palm Beach/Florida
Gotcha! With chlorine, too much is better than too little.
WAY better. Ask me how I know.

If you spend any time reading the forums here you will notice a recurring theme. All the guides and admins tend to run their FC a little hot. They always keep an extra buffer. All of us amateurs tend to run on the low side. Guess which group gets algae outbreaks.
 

Paultex6223

Member
Jun 12, 2015
9
Round rock texas
Ok so Tuesday night I added 1.5 gallons of liquid chlorine (that was all I had left) and let the pump run all night. Wednesday morning I checked and chlorine level was about 5. Added nothing yesterday, checked chlorine again this morning and in 24 hours I’m at 0, again.
 

jimbethesda

Gold Supporter
Jul 2, 2018
435
Austin, TX
Ok so Tuesday night I added 1.5 gallons of liquid chlorine (that was all I had left) and let the pump run all night. Wednesday morning I checked and chlorine level was about 5. Added nothing yesterday, checked chlorine again this morning and in 24 hours I’m at 0, again.
This time of year, in your climate, with a CYA of 30, losing 5PPM a day is a little high, but not unheard of. I’m currently losing about 4ppm a day and have a CYA of 80. You should aim for a chlorine level higher. If your min is 2, then bring your chlorine up to at least 7 (I would do 8) so that you never run the risk of going below 2.

Since you’ve let your chlorine go too low several times, you might have a beginning of an algae bloom. You might need to perform a SLAM. I would do an OCLT first. Perform the Overnight FC Loss Test (OCLT) - Trouble Free Pool
 

Chasarms

Silver Supporter
May 8, 2020
344
Dardenne Prairie, MO
Ok so Tuesday night I added 1.5 gallons of liquid chlorine (that was all I had left) and let the pump run all night. Wednesday morning I checked and chlorine level was about 5. Added nothing yesterday, checked chlorine again this morning and in 24 hours I’m at 0, again.

If your pool is fully exposed to the sun all day with CYA of 30, losing 5 ppm in 24 hours is not unheard of. It is also likely that because the pool has been frequently below FC targets, you have organics (algae) causing chlorine consumption. You don't always see Algae. By the time you see it, it's been there a while.

You can't add a large quantity and then expect to not have to add daily. When you add chlorine over targets for a given CYA, it will degrade much faster because there isn't enough CYA in the water to stabilize it.

If you don't want to add Chlorine manually daily, you should look into a SWCG or an automated liquid pump. I have a pump. It works great.
 

Dtkokay

Well-known member
Dec 31, 2019
305
Houston, Texas
Ok so Tuesday night I added 1.5 gallons of liquid chlorine (that was all I had left) and let the pump run all night. Wednesday morning I checked and chlorine level was about 5. Added nothing yesterday, checked chlorine again this morning and in 24 hours I’m at 0, again.
The minimum FC should be treated as a floor value, meaning don't ever let your value go below that. Rather than ping pong between 5 and 0, you should keep your pool between 5-10. In other words, add 3 gallons of FC now to bring it to 10, which will naturally drop to 5 for your pool. Then you can add 1.5 gallons per day going forward. Keep some FC in your pool all the time.
 

anotherpyr

Well-known member
Jun 22, 2007
92
Columbia, MD
I second the pool math app if just for the effects of adding. It helps me compare chlorine by ppm of chlorine per dollar for my pool. The high cost of chlorine due to the pandemic have made 15% from the pool store a better deal than 6% elsewhere. The 10% the nearby Walmart has is at best 7% now based on the date on the jugs. So it’s not a good deal.

I guess I should add that I have to compute the cost manually. The app just gives me the result of adding the chlorine so I can then figure out the impact of $1 on chlorine level.
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,180
Central California
@Paultex6223, you up for a little tough love? We can help you with this issue, it's likely very simple what's going on, but ya gotta meet us half way, not just keep posting that "it happened again." Start here, it's important to our process: Read This BEFORE You Post - Trouble Free Pool Please do everything asked for.

Next is to perform the Overnight Loss Test, as I don't see in your thread where you've done that yet.

With a pool you've somewhat neglected (I know you didn't mean to, but you have), you may not have the luxury of waiting it out or contemplating it for several days. It's been suggested that you likely have algae in your pool. If you don't get on this, like now, what a few days ago was a simple fix can quickly turn into a full on algae bloom that can take a week or more to straighten out, and cost a considerable sum in chlorine.

And one more spank for good luck, if you have a pool (even an SWG pool), you don't get to run out of chlorine. Certainly not in the middle of summer. You need to have an adequate supply at all times, because algae can happen just that fast. And that is never more true if algae is suspected (and for now, for your pool, algae is suspected!). So go out and stock up with a good supply, all with fresh dates and lets get this fixed.
 
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