FC dropping fast, TA rising

[agonista]

i've been maintaining my pool following TFP methods since roughly july of last year, but i have recently encountered a scenario i'm having trouble figuring out:

- FC drops super rapidly, roughly 16 ppm on recent sunny days while running SLAM with no substantial visible algae
- TA appears to be rising notably during this process, going from 150 to 170 within a few days

i am struggling to keep my pool sufficiently chlorinated and algae free as a result of the rapid depletion of FC. historically, i have seen roughly a 3.5 ppm FC loss on a sunny day with CYA at roughly 40 ppm.

over the past couple weeks, i have noticed a rapid acceleration in the FC loss rate during the day in my pool. for many months, i have seen roughly 3.5 ppm FC loss on a sunny day during the warm season, but i was seeing a loss rate more like 6-7 ppm FC a few days ago. i currently have CYA at 50 ppm.

just today, i had FC at 20 at 0730, FC at 9 at 1330, and FC at 4 at 1730. at 1730, i had a TA of 170 and CH of 230. when i tested TA several days ago, it was at 150, so it is increasing instead of remaining nominally stable, as it has done historically.

i also just noticed the presence of what appears to be 2 nails or similar iron/steel pieces at the bottom of the pool. i will have one of my kids dive and fish them out shortly.

i have SLAM'ed this pool 2 or 3 times previously without event, and i did not experience this acute FC loss unless there was a substantial amount of algae present, which there is not in this case.

could this be the result of either the metal pieces or potentially FC reacting with pool plaster? i do have a decent amount of pool tiles that have come loose since i have been at this house.

thanks for reading

 

[ajw22]

How long have you had FC at 20?

It can take 2 or 3 or more weeks of FC at SLAM levels to eradicate algae when the pool looks clear.

 

[agonista]

How long have you had FC at 20?

It can take 2 or 3 or more weeks of FC at SLAM levels to eradicate algae when the pool looks clear.

i have only had it at shock level for 2 days, but i have burned through a huge amount of liquid chlorine as a result of this FC loss rate.

even when my pool was super green last spring and i did my first slam, it took roughly 5 days to go from unusable to clean.

when i cleaned the filter, it wasn't particularly dirty either.

 

[newdude]

Why were you slamming this time ? Was it cloudy or just preemptive?

 

[ajw22]

Every time is different.

Assuming your CYA 50 test is goo then the chlorine consumption shows you have algae. You need to keep up your FC and you will see your FC drop once you break the back of the algae.

 

[agonista]

Why were you slamming this time ? Was it cloudy or just preemptive?

i was slamming because i had accelerating FC loss, which led to episodic algae growing on the areas of the pool that get the most sunlight. i did not have acute algae growth that had triggered my slamming previously.

in short, my slam was a result of my not seeing any other things to blame the FC loss on.

 

[ajw22]

Algae is algae and none should be in the pool. Episodic is no better then acute and neither should be tolerated.

 

[newdude]

in short, my slam was a result of my not seeing any other things to blame the FC loss on.

Overnight Chlorine Loss Test is what you do there.

If you hold FC with no UV, your CYA isn't high enough for the current demand.

Or you have a flat out reason to slam proving organics with overnight FC loss.

 

[fidn37484]

FC drops super rapidly, roughly 16 ppm on recent sunny days while running SLAM with no substantial visible algae
- TA appears to be rising notably during this process, going from 150 to 170 within a few days

It should depending on what chlorine you’re using. Liquid chlorine 10-12% will have a PH of 11-13 in a 1% solution. it should increase your ph and alkalinity.

 

[JJ_Tex]

It should depending on what chlorine you’re using. Liquid chlorine 10-12% will have a PH of 11-13 in a 1% solution. it should increase your ph and alkalinity.

Liquid chlorine has no bearing on TA and PH. Even if the OP added a full gallon to their pool, it would be way more diluted than the 1% you referenced (.00003 to be exact)

 

[fidn37484]

Liquid chlorine has no bearing on TA and PH. Even if the OP added a full gallon to their pool, it would be way more diluted than the 1% you referenced (.00003 to be exact)

Yes it does over time it will increase your ph

 

[newdude]

Yes it does over time it will increase your ph

Lifted from the TFP Wiki :

What is the Effect of Adding Liquid Chlorine on pH?[edit]​

It is a myth that liquid chlorine will raise pH. The myth is based on a misunderstanding of chlorine chemistry.

Adding liquid chlorine to water can cause a temporary increase in pH which is usually offset by the chlorine reacting with organics and biological matter which are acidic (creates a proton) reactions. Thus, on balance, the net chlorine reactions are pH neutral.[7]

Most retail and commercial liquid chlorine products contain a small excess of lye from the manufacturing process but this amount of OH- is minimal and does not change the pH with normal levels of liquid chlorine use.

If one were to add significant amounts of liquid chlorine (for example, raising the pool water chlorine concentration to SLAM FC levels), then the pH rise would need to be offset by an initial lower of the pH with acid. This is why TFP requires a pool owner to adjust their pH down to 7.2 prior to starting the SLAM Process.

Adding liquid chlorine DOES increase the pH at first, however as it's used up the acid that's created lowers it back down to where it was before......thus equaling each other out making it pH neutral.

 

[JJ_Tex]

Yes it does over time it will increase your ph

nuh uh

PH - Further Reading

www.troublefreepool.com

Newdude beat me to it. Sure, a very immeasurable increase then stabilization back to nearly neutral. Not enough to notice or even measure for a DIY pool owner.

 

[fidn37484]

nuh uh

PH - Further Reading

www.troublefreepool.com

Newdude beat me to it. Sure, a very immeasurable increase then stabilization back to nearly neutral. Not enough to notice or even measure for a DIY pool owner.

When you add liquid chlorine there is an an increase of hydroxides which increases alkalinity. When it’s done oxidizing the increase is less but can add up over time. He’s so called “Slamming” looks like a repackaged form of breakpoint chlorination to me. or sped up version if you will. His anecdotal test results concur with this.

 

[JJ_Tex]

We are splitting hairs at this point, and taking away from the OP's real problem of losing chlorine and possibly having algae.

I would encourage you to start a new thread in the Deep End forum, where the big brains live, and can talk about chemistry without derailing someone's thread. You can also use the search feature and find some older threads talking about pH and liquid chlorine, especially ChemGeek. Interesting stuff, just not for this particular thread.

Back to the OP and I will second the recommendation to do an OCLT as that will for sure tell you if you have algae or not.

 

[mgtfp]

When you add liquid chlorine there is an an increase of hydroxides which increases alkalinity. When it’s done oxidizing the increase is less but can add up over time. He’s so called “Slamming” looks like a repackaged form of breakpoint chlorination to me. or sped up version if you will. His anecdotal test results concur with this.

Adding chlorine will raise pH. But the processes that "consume" FC are acidic. By the time FC is down to where it was before the chlorine addition, pH is also back down to where it started. There can be a small effect due to excess lye in the bleach. But in the meantime, pH will have risen due to CO2-outgassing which is the dominant driver for pH-rise.

The complete chlorination cycle with liquid chlorine is pH- and TA-neutral. Same for chlorination with SWGs.

 

[agonista]

Overnight Chlorine Loss Test is what you do there.

If you hold FC with no UV, your CYA isn't high enough for the current demand.

Or you have a flat out reason to slam proving organics with overnight FC loss.

oclt resulted in 0.5 FC loss with filter running continuously overnight, 11.5 -> 11.0.

it would seem there is no algae problem currently.

any thoughts on what else it could be? my TA is higher than historically, it's typically 90-120.

 

[newdude]

oclt resulted in 0.5 FC loss with filter running continuously overnight, 11.5 -> 11.0.

it would seem there is no algae problem currently.

Still nothing visible ? No isolated appearances?

any thoughts on what else it could be?

The sun has been hitting many early this year. I'm already at peak season CYA levels and your UV whoops mine.

If there's no algae, seen or tested, I'd add 10 CYA and road test it. Get another test today for funsies and pour the sample back and forth as many times as you need to feel good about it. I have used best 5 out of 7 many times, if not every time.

my TA is higher than historically, it's typically 90-120.

That'll pull up the PH a bit faster but irrelevant to the FC loss.