CC inconsistency...can anyone tell me what is going on?

[brian4110]

Opened my pool last weekend to a green swamp (bought the house this winter so I had no control over the pool closing).

I've been shocking the pool ever since, per instructions in pool school. I use the pool calculator and test with a TF100. Ok, all good so far.

What is puzzling me is that when I test in the morning, CC are at or near 0, but by the end of the day they skyrocket. What causes that? Is the daylight sun helping the chlorine battle the nasties? Where does the CC go overnight? I suspect I may have an ammonia problem (haven't tested) because CYA was 0 at opening and the pool was filled with crud that I have done my best to remove.

Here is my test history:
@ pool opening last Saturday (May 18)
FC: 0
CC: 0
pH: 7.6
CYA: 0
TA: 90
CH: 340

So I immediately started shocking (bleach) as well as adding enough CYA to get to 20 ppm.

Yesterday is a good example of what I'm talking about. At 7 AM I tested and found FC=9 and CC=1.5. So I added a enough bleach to get back up to shock level (11). I was out all day working the polls (election day) and didn't get back until 11 pm and found FC=2 and CC=7. Dumped enough chlorine to get back to shock level. This morning, at 7:30am I tested and got FC=13 (oops, overshot) and CC=0!

My pool gets full sun all day long. I still have a bit of fine debris on the floor of the pool. I can see the bottom of the pool and the water is clearing slowly.

Anyone have any idea what is going on with the FC/CC levels? I understand I might be losing FC during the day to the sun, but I'm not losing much at all at night. And why does CC skyrocket during the day and plummet at night?

 

[woodyp]

My best explanation is that, as you kill the algae, some of that death is converted to CC as a byproduct. Maintaining the shock level consistently will kill it faster and break down the CC levels.

 

[JasonLion]

Chlorine is lost rapidly to sunlight during the day, so it quickly falls low enough that CC can form. At night you can maintain higher FC levels which further break down the CC and get rid of it. This will stop happening when you get CYA high enough to get some protection from sunlight.

 

[Lowarea]

why do you suspect an ammonia problem?

My circumstances are similar to yours and I'm new to opening a pool as well. I'm asking simply to learn more.

My opening is going well. Still at shock levels but FC and Cc is stabilizing.

 

[brian4110]

I suspected a possible ammonia problem because I'm pretty sure the previous owners were heavy users of trichlor which contains CYA, yet when I opened the pool this year my CYA was 0. From reading the board, this might indicate a bacterial problem whereby bacteria was comverting the CYA to ammonia.

why do you suspect an ammonia problem?

My circumstances are similar to yours and I'm new to opening a pool as well. I'm asking simply to learn more.

My opening is going well. Still at shock levels but FC and Cc is stabilizing.

 

[brian4110]

Ah! I didnt make the connection that hi levels of fc would break down the cc. In fact, I was assuming the opposite, that high levels of fc would correspond to higher levels of cc since more chlorine was available to combine with organic material.

Chlorine is lost rapidly to sunlight during the day, so it quickly falls low enough that CC can form. At night you can maintain higher FC levels which further break down the CC and get rid of it. This will stop happening when you get CYA high enough to get some protection from sunlight.

 

[duraleigh]

A note to all new testers....don't worry about ammonia.

It is an uncommon experience and will be characterized by massive consumption of chlorine. If it happens to you, you will be pretty aware right away. For 99.9% of you, it isn't worth fretting over.

 

[JasonLion]

The key indication that you have an ammonia issue is that FC will never go above zero. CC may well climb quite high, but FC will never be above zero (until you burn off all of the ammonia).

In this case FC was well above zero at some points, so not an ammonia issue.

 

[brian4110]

Thanks experts!

My CCs continue to jump all over the place, but I am doing my best to keep FC at shock levels (hard to do with full sun on the pool and a 8-6 job). Slowly but surely, the water is clearing.