Losing FC fast

[elmorage]

I am really struggling to keep my FC in the recommended range. I test the water in the evening when the sun is off the pool and add what the pool math app recommends to get me to a FC of 7, the high side of the range for my cya of 40. The last 2-3 days when I test in the evening I am below the recommended minimum FC of 3, so i started bumping to 8, then 10, and I still don't make it until the evening. Tonight I tested the water and my FC was only 2. Not only am I going through tons of bleach but I don't want anything to start growing when I fall below the minimum.

I think I have this right from reading posts here but I want to make sure... I tested the water again tonight in the dark and got a reading of 12.5 and plan on checking again before sunrise tomorrow for the OCLT. If I lose more than 1 I need to slam, but if I lose less than 1 does that just mean the sun is too aggressive on my chlorine and I need more cya? Our pool is in full sun, all day long from about 8am to 7pm.

 

[jblizzle]

Please add your location to your profile as that might help us answer your question.

When did you last check the CYA level?

You have the OCLT correct, as well as the possible outcomes and corrections

 

[elmorage]

I am in NY, about 90 mins north of the city. I checked the cya about two days ago and it seemed to turn in the high 30s which I rounded to 40. I had fresh water for the install about 10 days ago and have been increasing it slowly so I don’t overdo it.

 

[elmorage]

So we passed the oclt. It was pretty close to 1.5 loss, but I think it was that last level of light pink and gave it one more for crystal clear to get to a loss of 1. Close enough to call it a win.

So is the cya the only other possibility for losing so much fc during the day? Is 40 too low for a pool that gets 10-12 hours of full sun?

 

[jblizzle]

If the losses are not to something in the water, as ruled out by OCLT, then only other source of loss is the sun. Lots of intense summer sun would warrant a higher CYA.

 

[elmorage]

Started the day at 11.5 at 6:15am and at 7:15pm we were down to 3. Seems like an awfully big drop.

 

[jblizzle]

No use? No random people peeing in the pool? ?

Agree that seems high, although the higher you raise the FC, the more ppm you will lose. Think of the CYA as protecting a % of the FC.
At the same loss rate, if you started at 8ppm, you may only be down to 2ppm, a loss of 6; but starting at 11.5 you lost 8.5 which is the same % loss.

Are you sure the CYA is not down around 30ppm or less?
Raising the CYA should decrease the % of FC lost to the sun.