Why daily bleach additions?

Jump to latest Follow Reply
F

fralo

0
Aug 25, 2016
49
Pace/FL
So here's a very newbie question. If CYA is a stabilizer it should maintain whatever the corresponding FC level is according to the CYA/chlorine chart, right? Why then the need to add anymore bleach at all?

I know that this is a sill question but I just wanna make sure my thinking is correct. Even though CYA is a stabilizer the FC level will still diminish, just not as quickly, right? So daily bleach is still needed.
 
In a pool with zero CYA, the FC has a half life of about 20mins or so. So, in about 2 hours, the FC is entirely depleted.

In a pool with CYA, that half life can approach almost 8 hours (at high CYA). Therefore most of the FC will remain in the water.

CYA is both a stabilizer AND a buffer for chlorine. It's buffering ability is what makes swimming in a (properly) chlorinated pool comfortable.
 
Hi,
the question you asked is a good question, but it's not the easiest to answer without having a lot of knowledge about the actual chemistry. So, I have posted below a reply by Chem Geek on happens at the chemical level.

Following that, a link to the thread so you can further look at what happens chemically if you wish to. But to start with, not 100% of the chlorine is bound by CYA.. As that unbound chlorine gets used up, the chlorine which is bound by CYA gets released....

From Chem Geek
It comes right down to chemical equilibrium between chlorine and CYA vs. chlorine bound to CYA where the equilibrium is shifted much more to chlorine bound to CYA at normal pool conditions. The chlorine bound to CYA has minimal activity in terms of oxidation and sanitation. Because this is a chemical equilibrium, as chlorine gets used up, more is released from that bound to CYA and this happens relatively quickly and in the time of the FC test which is why the FC test really measures reservoir chlorine (that is, chlorine that is bound to CYA as well as that which is unbound). However, actual chemical reaction rates, including the rate of killing pathogens or algae, is dependent only on the actual chemical species doing that killing which is hypochlorous acid (for oxidation reactions it is sometimes hypochlorite ion, but it is not chlorine bound to CYA)......

You can read the whole post here. See No. 4.
FC - Concept of
 
So please tell me if the way I am currently maintaining my pool is okay. In the evening I bring my FC level up to about 5 or so. The next afternoon it usually has been reduced to 3.5, and so I add about 25 oz of bleach. I have only been checking my FC level every 2 or 3 days lately.

I assume it's only normal for everyone to get used to their particular pool and know about how much Fc level is lost over a days time.
 
You should also keep an eye on your pH.

I am assuming your keeping your target FC of 5 based upon the FC/CYA chart?

As a person new to maintaining your pool by TFP method, we recommend you really should test FC daily. If you let the FC get too low (relative to the CYA level), then you are being a bit risky. I know that 1.5ppm loss in a day doesn't sound like all that much, but thats a 30% loss of FC in one day.

And you are right, over time you will lean your pools apetite for chlorine and you can adjust your testing schedule. The only way to learn that though is by daily testing to start with.
 
Based on your pool volume, add enough bleach to increase your levels about 2 ppm daily (This is what I do). Then, on a weekly basis, I test to determine how much FC is in the pool. If I am over, I make adjustments then (usually skip a day or so). Although, daily I check PH and FC with the Taylor K-1000 (presence of chlorine) only.

If you add .5 ppm extra daily (because you burn off 1.5 ppm daily), by the end of the week, you will only be over by a little bit. Remember you loose a % and not a fixed amount daily.

Another important note is to brush your walls frequently in your pool to minimize the possibility of algae growing on the floors and walls. Intex Pools do not have the same circulation as other pools and you could have some dead spots. Please make sure that your daily additions are not in the middle of the day when the sun is beating down on the pool. Add either real early or late as the sun is coming down and have the bleach mix for a few hours or so.
 
5 is above my target FC. Yet I bring it to that every evening so that by the next day it will have drifted back down to around 3.5 - 4.0 and good for swimming. Am I doing wrong? My CYA was last at 30 so target is 4.
 
Any FC level, up to SLAM level for your CYA, is good for swimming. Target is what you want at all times. Letting it drop is asking for trouble. The minimum value is really only there so folks don't panic if they go a little below target.
 

Enjoying this content?

Support TFP with a donation.

Give Support
How is it possible to keep it at target level at all times if you only make 1 addition daily? I'm not "letting it drop". That's just going to happen automatically, right?

No, I don't lose more an 1ppm at night. I just finished my first SLAM a week or so ago, and tested that.
 
see answers in red.

fralo said:
How is it possible to keep it at target level at all times if you only make 1 addition daily? You can't keep it at target level at all times without an automated system to provide chlorine to the pool. But you can keep it from falling below the minimum level per the FC/CYA chlorine chart. You will have to add chlorine every day to keep it within the recommended minimum and target levels.

Pool School - Chlorine / CYA Chart

I'm not "letting it drop". That's just going to happen automatically, right? Yes. Chlorine is burned off by UV from the sun and from stuff that gets in the pool, like leaves, grass, bugs and other stuff. If you don't replenish it daily, it will go all the way down to zero in a couple or 3 days. The CYA just slows it down a bit. Without CYA you would loose all of your FC in 1 day.


No, I don't lose more an 1ppm at night. I just finished my first SLAM a week or so ago, and tested that.
Click to expand...
 
If you are getting full sun in FL you may want to bring your CYA up higher to maybe around 45ppm and keep your FC target at around 7ppm. That's what I do up here in IL which doesn't get your sun and I also have an auto cover. If I don't use my pool with the cover during the week I don't need to add chlorine for 3 days.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply