FC/CYA Ratio

[rmturner54]

I have done a lot of reading on this subject and am still a little confused.
My FC has gone from a 5 to 3.5 over the course of a week. The latest readings are as follows.
This morning at 10AM
FC 3.5, system was not generating at time of test due to 50% setting
PH 7.4
TA 120
CH 230
CYA 40-45, still not sure how accurate my readings have been
Wtr 83 deg
Salt 3500
% out 50%

So what is the correct chart or numbers to use. i read one article where is says Most saltwater chlorine generator (SWG) pools appear to prevent algae at a minimum FC level of 4.5% of the CYA level as compared with the roughly 7.5% of the CYA level shown in the "Min FC" column for manually dosed pools.
Having said that then 4.5% of my CYA level of 45= min FC of 2 which I know is probably too low.
My Aqua rite manual says to maintain a CYA of 60-80 with 80 the best and FC of 1-3.
Just want to make sure I am understanding what ratio to use for salt system.

 

[JasonLion]

4.5% is the correct number for a SWG pool.

I strongly recommend you raise CYA into the 70 to 80 range. That will greatly increase the lifetime of your SWG and make problems noticeably less likely.

Why do you say: "CYA level of 45= min FC of 2 which I know is probably too low"? FC of 2 should be fine with a SWG and CYA at 45, as long as FC never goes below 2.

 

[rmturner54]

By the math you are correct that FC of 2 is correct for a CYA of 45....I say too low because of the math using 4.5% and some of the things that I have read recommends a min FC of 3
Thanks about the 4.5% ratio number. That helps me confirm that I need to raise my CYA to 70. Once I do that then I have to deal with the PH going down. Pool math says 19 oz of stabilizer will raise CYA 20 and lower PH 0.38.
End results will be approx CYA 65 or so and PH of 7

 

[elwood58]

pH will go back up pretty quickly, as the SWG is a form of aeration and tends to make pH go up anyway.

 

[rmturner54]

Just added 20 oz of stabilizer.

- - - Updated - - -

I forgot about SWG being a form of areation...still learning this stuff...thanks

pH will go back up pretty quickly, as the SWG is a form of aeration and tends to make pH go up anyway.

 

[JasonLion]

I did CYA at 45 and FC around 2 for several months a few years ago, never had any problems other than needing to set the percentage higher than what I use these days.

 

[jblizzle]

And by raising the CYA and shortening the run time, you not only prolong the lift of the SWG, but you will also slow down how fast the pH rises.

 

[rmturner54]

So what % are you using Jasonlion along with pump run time these days compared to previous?

 

[JasonLion]

Many different things have changed since then and my memory is a little vague. If I remember correctly the percentage went down to some where between half and two thirds of what it had been. Though at this point I can't remember where in that range it was.

 

[rmturner54]

What kind of run time we talking about. I am at 12 hours a day with a very efficient variable speed pump

And by raising the CYA and shortening the run time, you not only prolong the lift of the SWG, but you will also slow down how fast the pH rises.

- - - Updated - - -

 

[rmturner54]

Many different things have changed since then and my memory is a little vague. If I remember correctly the percentage went down to some where between half and two thirds of what it had been. Though at this point I can't remember where in that range it was.

what is your runtime/ouput now. i know your poolsize in much larger than mine

 

[JasonLion]

It is pointless to try and compare actual SWG percentages. They vary radically from pool to pool.

Most pools are fine with four hours of pump runtime, sometimes a little more.

 

[rmturner54]

Do you think my 12 hours of run time is too much. I have no shade so my pool gets unobstructed sun all day

It is pointless to try and compare actual SWG percentages. They vary radically from pool to pool.

Most pools are fine with four hours of pump runtime, sometimes a little more.

 

[mas985]

Yes, 12 hours is pretty long and probably 3x more than what you need. I have a link to a study in my signature which shows that most pools don't need more than about 3-4 hours of run time per day. Assuming of course that your SWG can keep up with that short of a run time so you may need to run longer just for the SWG.

 

[rmturner54]

That makes perfect sense on the run time. Once I get the CYA level established better then I am going to back the pump time off to 8 hours. and see what happens. And assuming that my swg can maintain the FC demands. Since my % out is at 50% that gives me a lot of wiggle room, unlike one thread I was just reading where his % out was 100. You had just posted on the thread.....ouch!! is all I can say.
I'll have to read the study in your signature.

 

[rmturner54]

Since adding stabilizer on the 6th to raise my cya it has rained several times. I did get a chance prior to going back to work on the 10th to check the cya it was 65. Since the rain my wife tested and the FC was 3.5 and cya was 55 to 60. By the chart I am ok. Should I still try to get it 70-80?

 

[jblizzle]

The higher CYA will let the SWG not run as much which extends its life and slows the pH rise. Up to you.

 

[rmturner54]

Thanks for the reply and input....I was thinking about getting wife to add some stabilizer and raise it to 70to80

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