FC drop

[schutzk21]

Hello everyone. I have a CYA of around 45 and I had a couple of questions.

The past few days, I have been bumping my FC up to 9 each night. When I get home today from work (6:15 PM) the FC was tested at 4.5.
I have the Taylor K-2006 kit. I know I have passed the SLAM test because I am losing less than 1 FC overnight.

Is this too much of a drop each day? (FC of 9 to 4.5?) Is this because I am bumping the FC up so high at night? I just read over the CYA/FC chart again and noticed that the target FC for a CYA of 45 is 5.175.

So, if the the FC starts at 9, does this mean it will drop faster as opposed to starting it around 7 FC? I am worried that if I start it at 7 that I will drop below the minimum FC (3.375). What do you believe would be an ideal target at night when I add bleach? I get a lot of sun on the pool 'til about 5:00 PM. Your help is much appreciated!

 

[jblizzle]

I assume your water looks crystal clear?

For that CYA, the minimum FC is 4ppm (see [FC/CYA][/FC/CYA]) ... so you have to raise it high enough each day that it will not drop below 4ppm by the next time you test and add chlorine. I think you have this idea correct.

A daily loss of 4.5ppm does seem on the high side though ...

 

[schutzk21]

Yes, the water is crystal clear. Do you think if I start off at around 7.5, my loss will be less and drop slower?

 

[jblizzle]

One way to think about the FC/CYA is that the CYA level will protect a % of the FC. You seem to be seeing a 50% loss in a day (which is right around the rule of thumb for a CYA in the 50ppm range). So, if you start at 8ppm, you would lose ~4ppm. Start at 7ppm, you might only lose 3.5ppm ... etc.

- - - Updated - - -

You could always raise the CYA level some ... and then maybe your FC losses would drop to ~40% a day

 

[schutzk21]

So if I kept the CYA at 45, it would probably be best to have the FC at around 8 when I am adding bleach at night. This will cost me around $60 per month in bleach. Does that seem too high to anyone else? I guess it isn't that bad.

 

[jblizzle]

4ppm daily loss is on the high side of normal. Bump the CYA up to 60ppm and you might lower the losses ... just make sure the FC stays in range to avoid algae and the SLAM process.

If you could add your pool details in your forum signature, that may help us help you in the future.

 

[wjr75]

I'm seeing the exact same thing that you are seeing this year. In years past I have not dropped the FC as much in direct sun at 45ppm CYA. I have a auto cover and don't drop more than .5ppm when closed during the day. I just started to bump up my CYA a little by adding some tri-chlor tabs. Kinda of a head scratcher this year. I bring my FC up to around 9 to 10ppm at night before closing my cover.

 

[schutzk21]

I'm seeing the exact same thing that you are seeing this year. In years past I have not dropped the FC as much in direct sun at 45ppm CYA. I have a auto cover and don't drop more than .5ppm when closed during the day. I just started to bump up my CYA a little by adding some tri-chlor tabs. Kinda of a head scratcher this year. I bring my FC up to around 9 to 10ppm at night before closing my cover.

Very interesting. Maybe you and I can compare our experience. I live in the Chicago suburbs. I see you also are in Illinois. I have a 45 CYA and maybe with the hot weather these past few days, a drop of 50% isn't so strange. I did the OCLT last night. Tested it at 9.3 FC at 9:30 PM and woke up at 5:15AM before the sun can start beating down. I was at 8.6 so I lost 0.7 overnight. What do you usually lose overnight?

 

[jblizzle]

Very interesting. Maybe you and I can compare our experience. I live in the Chicago suburbs. I see you also are in Illinois. I have a 45 CYA and maybe with the hot weather these past few days, a drop of 50% isn't so strange. I did the OCLT last night. Tested it at 9.3 FC at 9:30 PM and woke up at 5:15AM before the sun can start beating down. I was at 8.6 so I lost 0.7 overnight. What do you usually lose overnight?

What are you testing with? 9.3 is an odd FC number.

 

[spinPHD]

Just wanted to point out that it's best to read CYA in increments of 10. So with 45, you round up and have a CYA of 50.

 

[camueller]

I'm wondering if you are getting an accurate result on the CYA test. I'm also in IL, down near St Louis, and was having a similar problem earlier this year until I realized my CYA level wasn't where I thought it was. I got the CYA standard solution from TFTestkits to get an idea of what I was looking for, and then tested again and found out my CYA level was below 30ppm. I bumped it up to 40ppm and am only getting about 1ppm loss per day with my cover on and maybe 2 with it off. I should probably run at 50ppm CYA considering my pool is in full sun all day long, but if my chlorine use stays like this why bother?

 

[schutzk21]

I have the K-2006 kit. I wrote 9.3, but its more llke 9.5. The water was very lightly pink in between drops.

 

[schutzk21]

I'm wondering if you are getting an accurate result on the CYA test. I'm also in IL, down near St Louis, and was having a similar problem earlier this year until I realized my CYA level wasn't where I thought it was. I got the CYA standard solution from TFTestkits to get an idea of what I was looking for, and then tested again and found out my CYA level was below 30ppm. I bumped it up to 40ppm and am only getting about 1ppm loss per day with my cover on and maybe 2 with it off. I should probably run at 50ppm CYA considering my pool is in full sun all day long, but if my chlorine use stays like this why bother?

Interesting. Is this a solar cover or do you have an IG pool with a regular cover? Mine is AG.

 

[camueller]

Interesting. Is this a solar cover or do you have an IG pool with a regular cover? Mine is AG.

Mine is an IG with a solar cover on right now. I keep it on the pool unless we are going to be swimming.