Pros / Cons: Low FC+ CYA vs High FC + CYA ??

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squibcakes

0
Sep 20, 2015
55
QLD Australia
Assuming the correct ratios of FC and CYA in a SWG pool, what are the pros and cons of having high FC vs low FC?

I try to maintain FC:6 CYA:80. Why would 4:60 not be recommended?

Also why do "Most saltwater chlorine generator (SWG) pools appear to prevent algae at a lower minimum FC level compared with the minimum FC column for manually dosed pools."?

Surely Cl is Cl regardless of how it is regulated in the pool? Is this just based on owner experiences?


Cheers
Squib
 
Hi Squib,
Low FC/CYA vs High side.

Its all about how much FC is lost to UV. UV eats up chlorine quicker than anything else. So, depending on where you are in the world, your UV exposure may be higher or lower than someone else.

For example, someone in the hot desert would be exposed to higher levels of UV as someone in a more moderate climate.
So protect the FC from UV burnoff, the desert dweller would want to keep his CYA at a higher level than the person in the more moderate climate with less UV exposure.

Determining which CYA/FC for your particular location is mostly a matter of Trial and Error by testing often.
If you top off the FC at recommended level in the a.m. and and in the evening you are below the minimim FC, and you do not have any orgainics consuniming the FC, then you are a candidate for increasing your CYA. Repeat the scenario and test until you find the sweet spot where your FC remains between the max and min recommended level over the course of the whole day (24 hrs).

As for the SWG using lower FC,
the Liquid chlorine user doses a batch of Chlorine once a day, over the course of the day the FC drifts down to the minimum recommendation, and repeat the next day.

If using a SWG, the TFP recommendation is for the SWG to generate chlorine for a short period of time multiple times a day. So instead replacing ALL of the used up FC at once, it replaces it little by little, as it's used up.

It isnt fully understood exactly why, but it seems that by dosing small amounts multiple times a day, you can keep the minimum FC requirement slightly lower than you can by dosing one big dose.

hope this helps,
 
:D Thanks for your response - that makes sense.

I can see now there would be a lot of variables that would effect how much UV a pool gets; shade from trees, summer has longer days etc

OK, I have some more tweaking to do on my TFP water balance. ;)

Cheers
Squib
 
Wow, what a great question and an even better answer. It confirms my suspicion that because I live in a very hot, sunny environment with no shade on my pool for most of the day that I would benefit from bumping my CYA from 50 to 70, thus keeping my FC between 5-8. I might get by with actually adding less chlorine this way.
 
I've read a few times now about the salt water generator cell being a super chlorination environment. The environment in the cell has a much higher concentration of chlorine that the pool. The dwell time is short but in effect the water passing through the cell is being super chlorinated.
 
The % of CYA binding to FC would be the same at higher CYA. The difference is that having the higher PPM of the CYA in the water itself seems to shield the UV from reaching into the pool as much (setting aside the binding to the chlorine). This is an assumption based on some observations in a bucket test and general TFP user feedback.

search for "shielding effect"
 
Hello Squib, my 2 cents is from reading before deciding my targets, including here at TFP, the pool forum, Ben Powell's site and Robert Birch's stuff (Uni Queensland prof). The shortest thread I could find here that sums up the reasoning is... Why is CYA kept higher with a SWG?. There's other more technical threads in The Deep End.

Two things are not fully understood, but have been experienced in countless pools. 1) Lower FC/CYA ratio with SWG is effective; and 2) SWC causes faster pH rise. The reasons are thought to be: 1) super-chlorination within SWC, and 2) increased outgassing, respectively.

There are also threads here describing experiments by TFP experts demonstrating that they need lower SWC run time at the higher CYA level, once the target FC level has been met.

So for me, I'm going with the TFP Pool School recommendations, because I want the higher CYA to reduce chlorine consumption and SWC run time. Running the SWC causes pH rise, so the less I run it, the less the pH rises. I can't measure or prove it (I only have one pool), but the experts here and elsewhere explain it all and I trust them. My numbers so far align really well with the understanding I got from researching it all. I keep my FC higher accordingly, but it takes less run time to maintain the level. Less run time means the cell will last longer, so I can save money on acid, cell replacement and electricity.

Now if only I could get some Queensland heat!
 
Thanks nlindelldc,
The higher CYA level may indeed help you maximize your FC efficiency and result in less Chlorine dosing.

The down side to increasing it to 70 however, is that if you happen to get algae, it will take a lot more chlorine to SLAM than if you had a lower CYA. This is why the TFP recommendation isn't higher. So, it will be important to maintain the FC to take advantage of a higher CYA level.

Also another morsel of food for thought of maintaining higher CYA. A lot of folks when going on vacation will use Chlorine pucks to provide FC while they are gone. But if you have CYA of 70, it might not be ideal to use Pucks because the will also add CYA.

So at the end of the day, it really all comes down to a balancing act of how to best maintain your pool for your own situation.




nlindelldc said:
Wow, what a great question and an even better answer. It confirms my suspicion that because I live in a very hot, sunny environment with no shade on my pool for most of the day that I would benefit from bumping my CYA from 50 to 70, thus keeping my FC between 5-8. I might get by with actually adding less chlorine this way.
Click to expand...
 
Divin Dave said:
Thanks nlindelldc,
The higher CYA level may indeed help you maximize your FC efficiency and result in less Chlorine dosing.

The down side to increasing it to 70 however, is that if you happen to get algae, it will take a lot more chlorine to SLAM than if you had a lower CYA. This is why the TFP recommendation isn't higher. So, it will be important to maintain the FC to take advantage of a higher CYA level.

Also another morsel of food for thought of maintaining higher CYA. A lot of folks when going on vacation will use Chlorine pucks to provide FC while they are gone. But if you have CYA of 70, it might not be ideal to use Pucks because the will also add CYA.

So at the end of the day, it really all comes down to a balancing act of how to best maintain your pool for your own situation.
Click to expand...

That is also a great point. I am currently doing a "vacation simulation" using pucks for a week and seeing how long I need to run my pump in order to maintain my FC levels. I have had to increase pump run time to almost 10 hours! I was shocked by that. When manually dosing chlorine I only run my pump a couple of hours a day!
 

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Wow lot of responses. Thank you. My head hurts now. Lol.

I know that with the higher FC / CYA my pool has never looked better and that is probably the answer right there.

(This is all interesting because I gave my SWG cell (first) clean the other day and have notice a big spike in the FC level so much so that I have had to turn the % down a lot to try and get my FC back on track. I'm really surprised that just tiny amount of Calcium on the cell can inhibit Cl production.)

I think in the name of science I will again run a lower FC just to confirm my suspicions.

Do you guys run lower FC in the off season? We just started Autumn and probly have a month left of swimming here in sunny QLD.
 
Off season chlorination requirement is going to depend on local climate, in general need for chlorine when water temperature is below about 55 degrees F is low, however it picks up quickly above 55F.

Ike
 
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