Trying to make sure I understand FC/CYA relationship

Jump to latest Follow Reply
T

TexKSAH

0
LifeTime Supporter
Aug 15, 2014
74
Austin, TX
Correct me if I'm wrong or over simplifying it. Just trying to make sure I fully understand FC/CYA relationship. What I know (or think I know) I learned here so I know you guys can clarify and clear up anything I'm still cloudy on....

FC = Active Chlorine (unbound and available to immediately attack any nasties) + Reserve Chlorine (Chlorine bound to CYA but can still be tapped into, just not immediately).

If this is a true statement, does anyone know what percentage (assuming there is nothing in the pool at the moment for active chlorine to attack) is active and what percentage is reserve for any given CYA level?
 
Not really unless you are saying that "minimum FC" would equate to "reserve Chlorine" and the difference between "minimum" and "Target" is the active chlorine. I don't want to make that assumption, but if that is correct, that does help.
 
OK, now to the question that has been nagging me but I think I have the answer now.

If I'm planning on trickling in liquid chlorine all day long (when the filter pump is running) using a Stenner pump instead of large doses, wouldn't it be better (less chlorine) to keep CYA at the lower level (around 30ppm for gunite in direct sunlight all day) instead of the upper end of the range (60ppm)?
 

Enjoying this content?

Support TFP with a donation.

Give Support
Actually I would suggest keeping it at the higher end of the range for the same reason as it is suggested for SWG pools. The higher CYA offers more protection from the sun. One reason a lower CYA is suggested for manually dosed pools is because it is much easier to miss a dose or two and end up needing to SLAM. It also gives a cushion for needing to use trichlor during multi-day trips. Higher CYA is suggested for SWG pools because the automation greatly decreases the possibility of needing to SLAM, so having less chlorine burn off in the sun is of greater benefit. So I would aim for 60 CYA if I were using a stenner pump.
 
I see your point Donldson and that explains why SWG users have a recommended higher CYA level.

I guess I was thinking if your adding small doses constantly throughout the day and night, you would lose less chlorine to the sun and you could improve on that by the lower CYA/FC and thus less chlorine use overall.
 
You are thinking the same thing I was at one point. What I had to realize is this; Higher CYA does not mean higher FC. It does mean higher base FC but NOT higher FC usage. Daily usage can be similar regardless of CYA level. (too a certain point, and oversimplified like crazy)
 
OK, then is there a way to calculate how much chlorine I will need to add per day to maintain the target level? I see the calculator to determine how much to "reach" a target, but not to maintain it. I guess that might be hard to calculate because of the myriad of factors that goes into it.
 
Is this a correct statement then (albeit very simplified and general)....

FC day-to-day usage is very similar regardless of the CYA/FC levels, but higher CYA/FC levels provide more protection due to higher reserve levels?
 
That's how I understand it.

The amount of chlorine needed to keep you at your desired FC is a closely held secret. No not really. :) It's a game of up and down until you find the sweet spot.

ChemGeek will probably have a very complex formula for it.
 
Yeah, I'm sure daily usage is noticeably different between sunny and cloudy days and swimmer load, etc. But in order to make sure I order the correct stenner pump, it would be nice to know what the expected daily chlorine need would be, at least in general.
 
Generally acceptable chlorine losses can vary depending on temperature, sunlight, bather load and other factors but with no bather load, full sunlight summer water temps and adequate CYA levels, somewhere between 2 and 4 ppm FC loss each day could be expected. Some days I lose 1 FC, others I lose 3. Is the pool covered? All these factors will change the FC daily demand. Take the volume of whatever concentration of bleach you're using, necessary to achieve between 1 and up to 6-8 FC and figure out if your pump could do that. In fact, you'd be better off if your pump could achieve that 6-8 ppm FC increase volume in 4 hours of total run time or less to reduce filter pump run time.
 
Ok, based on that and 3-4ppm loss per day, I can expect to need between 50-70 oz. per day.

The 45MHP2 can deliver between 1.0 and 15.3 oz. per hour.
The 45MHP10 can deliver between 2.6 and 53 oz per hour.

Either should work for just about any scenario of pump runtime/stenner runtime/FC need I can imagine I would need.

Thanks
 
TexKSAH said:
Ok, based on that and 3-4ppm loss per day, I can expect to need between 50-70 oz. per day.

The 45MHP2 can deliver between 1.0 and 15.3 oz. per hour.
The 45MHP10 can deliver between 2.6 and 53 oz per hour.

Either should work for just about any scenario of pump runtime/stenner runtime/FC need I can imagine I would need.

Thanks
Click to expand...

I went with the bigger pump so it can deliver it's chlorine in the least amount of operating time (I have mine come on 3 times a day for about 15-20 min per cycle). This should prolong the life of the pump and the tubing.
 

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