How much should FC go down in 1 day?

[Lannjo]

Our FC is almost consistently at a 4 or a 5 when I test in the evening. We add however much bleach pool school tells us (it seems to be a different amount every time). I enter an 8 for the goal for chlorine on pool math. But we can never get it to 8! What am I doing wrong? The pool looks great! Clear water. My CYA is 50.

Yesterday it was about 20 degrees cooler and it did rain. When I tested the water the FC was 6.5. But usually it's at a 4 or 5.

How much FC typically gets used up in a day?

 

[jblizzle]

2-4ppm loss every day is normal.

If you are only testing once a day, then that is at your minimum and need to be sure it is above the min listed for your CYA in the [FC/CYA][/FC/CYA].

If you would retest your FC 30-60 minutes after you add your bleach, you should be able to confirm you are hitting your target of 8ppm.

 

[Lannjo]

2-4ppm loss every day is normal.

If you are only testing once a day, then that is at your minimum and need to be sure it is above the min listed for your CYA in the [FC/CYA][/FC/CYA].

If you would retest your FC 30-60 minutes after you add your bleach, you should be able to confirm you are hitting your target of 8ppm.

Ok I just tested it again and the FC is 12. I added 82 oz of 10% bleach (per pool math). I'll test it again tomorrow night and see how much we lost.

 

[Lannjo]

I just tested my water this evening 6/6/18 @ 7:15pm and FC= 5.5.

Yesterday evening FC=4 so I added 82 oz of 10% bleach to get the FC to 8 (per pool math).
When I tested it 30 minutes later the FC was at 12. Great! (Kinda high but at least it went up).
But this evening it is back at 5.5. That seems like a lot to go down.
My CYA is consistently at 50.

What is causing the chlorine to go down so fast? It is very hot this week (I'm in Texas). I still have my chlorine floater with some tabs in it so I would think that would help some.
Advice?

 

[jblizzle]

Chlorine is only lost to Organics in your water and to the Sun. You can do the oclt to verify whether you have Organics in the water. If you don't, then your loss is to the Sun. The higher you raise the FC above the recommended levels for your cya, the more PPM of FC you will lose to the Sun

 

[Lannjo]

Ok so I did the OCLT this morning, and my FC was 8 45 min after adding chlorine last night and this morning (before sun rose) FC was also 8.

So is the sun really lowering my FC that much? My CYA is 50 and according to the chlorine/cya chart the target FC is 6-8 (minimum is 4).

I plug in 8 for my FC goal on pool math because I'm in Texas and it is HOT HOT HOT right now. Should I aim for FC of 10? We had a lot of kids in it this past weekend, but typically it's just 2 kids in the pool.

I guess I am within the "recommended range" with minimum FC at 4, but I feel like it's cutting it too close!!

 

[kellyfair]

You can safely swim up to SLAM level, so if you know you are going to have kids in the pool, add a bit in the morn8ng then again when kids are out (test first to see where you are). That should handle sunscreen and anything else the kids are adding to the pool!

 

[Lannjo]

We are averaging about a gallon of 10% bleach every 2 days. Is this typical?

 

[jblizzle]

How many FC PPM is that?

 

[Derb22]

A loss of 2-4 PPM isn’t unusual. If you go much higher than the recommended level your CYA can’t protect it so you will just lose more in that day. Try and find the right balance to hit the target high FC LEVEL in the morning and you should use a bit less bleach.

 

[Oly]

What you are experiencing is normal and normal is a moving target this time of year. Realize the summer solstice is June 21 this year and that is maximum sunlight (solar radiation) and that puts pressure on your FC. Soon the temps will rise including night temps and water temps will also rise putting pressure on your FC. Bather load is another factor as are windy days pushing dirt and debris into your pool putting pressure on your FC. A quality test kit takes away the guess work and assures you that your pool water is in the proper FC zone relative to your CYA. We should not assume or expect a consistent FC loss through the year or through out the week, rather confirm actual FC levels with frequent testing. It takes some dedication and forward thinking to keep a pool in balance but it is all worth it.

 

[CavVet]

Ok so I did the OCLT this morning, and my FC was 8 45 min after adding chlorine last night and this morning (before sun rose) FC was also 8.

Good morning Lannjo! Just to clarify, when you performed the OCLT, did you remove all methods of chlorination? I.E. the floating chlorine dispenser?
i'm also in TX, and my pool is shaded until 1pm or so, but i am still losing approx. 2.5ppm of chlorine per day.

 

[Lannjo]

Yes we removed the floating chlorine dispenser during OCLT.

My pool gets sun from late morning to early evening so I guess losing 4 ppm of FC is to be expected. We kinda eyeball the measurements when we pour bleach in the pool. But when I did the OCLT my free chlorine did measure 8 which was my target so I guess we're doing something right!

Thanks for all your input! I was confused as to why going higher than my target FC (for my CYA levels) would be a waste, but I get now that the CYA protects the chlorine.