cholrine consumption

[dkbrat]

March 30th
FC 3
CC 0
cya 80 ( know it needs to come down, but on once a wk water restrictions)

Added I gal of 8.25% bleach

March 31st

FC 4.6
CC 0

Did OCLT test at 7:20 pm

April 1st

Tested at 7 am

FC 4.4
CC0

Added 1 gal bleach

April 2nd

FC 4.8
CC .2

Added 1 gal bleach


Pool calculator only recommended 3qts today. I have been adding the full gallon. What is going on? I didn't lose much over night. Is this a abnormally high amount of chlorine to be going through during the day. Water is about 64 to 68

 

[jblizzle]

I assume you are actually adding one 121 oz bottle of 8.25% bleach which is not a full gallon?

In a 19k pool, that should add 4.2ppm of FC. So losing ~4ppm each day with a CYA that high is a little surprising.

But, could it be that the bleach is weak and/or the pool is larger than you think and/or your CYA is not really that high?

Why not retest the FC level an hour after you add it (with the pump on) and see what FC level you are achieving?

Also note, generally the OCLT is performed at higher FC level closer to SLAM level.

 

[JasonLion]

1 gal of 8.25% bleach in 19,000 gallons will raise FC by about 4.5.

Yes, with fairly cold water and a CYA of 8 it is unusual to be using that much chlorine each day.

I can think of a couple of things that might be going on. Here are the two most likely: CYA might be lower than you think. The bleach might have lost more strength than normal, i.e. have a much lower concentration of chlorine because it is old or was stored at high temperatures.

 

[Smykowski]

If your CYA is at 80, your FC is too low. You should be aiming for 9 or 10, and putting more bleach if it gets to 6.

 

[dkbrat]

Yes, I am using the 121 oz bottle.
I retested and FC 8.6. So how many ppm should I be losing? At least this bottle seems to have good strength. I store inside, and usually buy 3 or 4 bottles a trip to Home depot.

I thought testing after sun down and before sun up let's you know if you need to slam due to chlorine loss overnight.
I have trouble with the cya test. Two times I thought I was in the 50 to 60 range, but I think the water was too cold. I let the mixture sit in the sun for 30 min before I did the reading and came up with 80. My CYA was 360 when I started the BBB program in Aug 2013. So I am making progress.

- - - Updated - - -

If your CYA is at 80, your FC is too low. You should be aiming for 9 or 10, and putting more bleach if it gets to 6.

Pool calculator lists 6-11

I always add the amount indicated and more frequently add a bit more than stated

 

[JasonLion]

With CYA around 80, FC starting the day at 8, and summer conditions, you should be losing 1 to 2 ppm/day. With the water cooler then less, presumably less than 1 ppm. On the other hand, if CYA was 50, I would expect you to lose 3 to 4 ppm/day at summer temperatures, 2 to 3 at cooler temperatures. All of these estimates are approximate, there are so many factors involved, I have to make guesses about several of them. In any case, with CYA at 50 you loss is higher than I expect but plausible, but with CYA at 80 it isn't plausible.

Leaving the CYA test sit for 30 minutes before reading probably invalidates the result. The cold water issues we are familiar with only take 2 or 3 extra minutes to go away. Cold water slows things down, but doesn't stop the reaction. The extra few minutes lets it resolve, when the normal 30 seconds doesn't always. You can still use the test results for several more minutes, but letting it go half an hour can cause other interferences.

 

[Smykowski]

But in all of your tests above, your FC was below the minimum.

 

[jblizzle]

But in all of your tests above, your FC was below the minimum.

YES! The 6-11 shows the range you should be in ... where 6ppm is the MINIMUM you should every allow the FC to get.

 

[dkbrat]

The CYA test is certainly the most difficult. I will test again on the next sunny day, perhaps I really am at the 50 range. If I understand Jason's post above, I could be losing 3ppm a day. We have had a few 80 degree days with full sun and wind. I really appreciate everyone's help. It was a long battle getting the CYA down with our water restrictions, and they have only gotten stricter since I started this program

 

[Patrick_B]

A loss of 3 PPM/Day would not be un-expected in the hot months and more with heavy use of the pool.