newbie question: Free chlorine question

[elteebee]

Got a question. I've been monitoring the pool chem with test strip for now. For a while, it's consistent

FC : 5
TA : 80
PH : 7.8

but yesterday and the test strip shows FC: 0 , so my question is, can FC drop from 5ppm to 0ppm overnight?
The weekend was hot (101F), so I did bump up the chlorine generator from 40% to 50% production. But the last few days the temperature dropped to 86-90F.

Initially I thought there's no FC anymore, but the historical chart shows that it doesn't drop from 5 to 0 , so now I am not sure if there's really no FC or the test strip is wrong.

I have the oreq 4 in 1 test strip that the pool builder provided for me. I need to get a better kit soon. Tried to get the ColorQ pro 7 but it's backordered.

Another question, does high FC causes PH to go high too? On the oreq instruction, it has a note that says if PH is high (purple color) then too much sanitizer. Is that a true statement? Come to think of it, I am just guessing it's 7.8 cause the color is hard to determine.

Appreciate the help.

regards,
Laurence...

 

[duraleigh]

Hi, Laurence,

Welcome to the forum. Test strips are frequently innaccurate and I would suspect them as the culprit.

For what it's worth, the ColorQ has some limitations as well.

A good drops based kit is invaluable to understanding and managing your pool water and is central in most of the pool chemistry advice given here.

Do you have a CYA test result? My assumption is your CYA is in the 60-80 range. If it's not that coulod possibly account for your Cl loss on a really hot day. I doubt it because you would've seen other indications. I still believe the best probable cause is the innaccuracy of the test strips.

 

[JasonLion]

Yes, FC can drop from 5 to 0 overnight, though that isn't common. This typically happens when you have algae. If the water is still clear then the SWG might be malfunctioning, or most likely the test strip is just wrong.

The PH tends to go up slowly with a SWG. PH can also read higher than it really is when you have a very very high FC level.

 

[elteebee]

Thanks for the reply. I'm gonna go get another test kit to verify the readings. Now that i think about it, the SWG was started when the weather is about 75-80F and SWG set to 40% and I get 5ppm. But i usually test it towards the end of the pump cycle.

The CF = 0/1 results was tested in the morning before the pump cycle. Also the weather has been towards 90-100 lately, so i am assuming, i should need to bump up the SWG production a little higher. I did do a test yesterday towards the end of the pump cycle too and found the CF = 3ppm.

I'll get the reading again with a better test kit today and adjust the SWG to 50% and see the results later towards the end of the cycle.

Being new, I am terrified of making the wrong decision and turn the pool green. At the same time I don't want to over do it and dump too much chemical into the pool either.

Thanks

regards,
Laurence...

 

[duraleigh]

Laurence,

Leslies FAS/DPD test kit, the Taylor K-2006 and my TF-100 are your best bets. Anything less will not test FC high enough or may even leave out the CYA test.

If your hesitant on what kit just now, go to the pool store and get them to test for free. Just don't purchase anything and then post the results up here. There's lots of folks here who will help you get started to a crystal clear pool all summer...without spending a ton on pool chemicals.

 

[elteebee]

Got my water analysed at pool store. My first trip and kind of interesting to see that they did analysis manually using taylor kits and such. I would have thought they use some kind of digital tester.

But here's my readings

FC: 1
TC: 1
PH: 8.0
TA: 80
CYA: 60
TDS: 2500
Phospate: 500
Salt: 3000

The guy there said reading good. SWG ph goes up over time and that I need to adjust it once a week. He calculated that I need 1 1/2 pint of acid to bring PH down.

One question I forgot to ask him, will adding acid brings down TA which seems to be perfect now.

Guess my fear was when i saw FC dropped from 5 to 1 overnight. I'll monitor it for now and see if it changes.

regards,
Laurence...

 

[duraleigh]

Using the drops based testing he did for you is still THE most dependable and accurate way to get good results....unless you have a LOT of money. He did a good job for you.

I would run the FC consistently at the 3-4ppm with your CYA of 60.

You don't say the size of your pool but 1.5 pints seems a little smallish to drop you back down around 7.2 which is where I suggest. Use Jasonlion's calculator in his sig to calculate how much muriatic you need.

Iff you want to make sure you have no algae, run your FC up to around 4-5ppm and then, after sunset, turn your SWG off, Get up early the next morning and see if your FC has dropped appreciably. If it has, you have a little algae working in your pool and you will need to shock.

 

[elteebee]

Based on the help here, I've bump up my SWG production to 65% and got 3ppm FC. I tested at sunset , then tested again in the morning and the FC is still at 3ppm. So I guess it's not algae. The pool builder did have someone balance the pool when it started and I believe they added chlorine manually the first 3 weeks. And my SWG only turned on by 3rd week and this week is really the 3rd week SWG being used. Also after checking my logs again, it didn't drop from 5 - 1 in a day, it really drop within 2-3 days. Guess I panicked for no reason. I guess I just need to adjust the SWG accordingly.

My pool is a 12000 gallon pool, I added 1.5 pints MA to the pool and the target proposed was 7.5. But after 24 hours, the pool PH still is at 8.0. Doesn't seems to make a different.

I got the MA from Home Depot which is a KemTek brand and it shows the active ingredient is 14.1%. I read somewhere MA active ingredients suppose to be somewhere around 30%? Is the calculator based on 14.1 or 30% active ingredients?


regards,
Laurence...

 

[Guest]

It's based on the stronger acid so you only added half of what you needed. It is important to keep your pH in line iwth a SWG. The best way to do so is to add the acid, wait aobut 3 minutes or so with the pump running and retest the pH. If it is still high then add more acid. A general rule of thumb is to add 1 pt per 10000 gallons when you add acid and then test. A good testkit is needed for this. The pH test on strips is notoriously bad!

 

[JasonLion]

My Pool Calculator is assuming 31.45% muriatic acid. If you have the 15.725% you need to double the quantity.