FC 4.5 yesterday and .5 this morning :(

[Jean-ji]

My FC was 4.5 with a .5 CC yesterday morning and the FC is 0.5 this morning. I was so surprised at the barely pink color instead of the deep pink, I got another sample. No luck, it was the same.

We had several torrential rains this past week. I’ve added bleach to bring it up rather than relying on the SWG, twice this week. My numbers have been steady for the past month with no problems, 4.0 is the lowest FC in the last month. I do the drop test every morning. Water is clear, I did all the maintenance and added salt and stabilizer yesterday morning.

I’ve been tweaking my SWG, going up and down between 30 and 40% for the past several weeks, and depending on sun and rain, I’ve been getting 6.5 to 4.0 FC readings each morning with 0 to .5 CC. When the heavy rains all week, I left it at 40% and used bleach to get it to 6 FC twice.

It looks like I will be slamming, but I don’t know why a sudden overnight loss like this with no CC problem and clear water happened. Obviously something is brewing, but why with good numbers? Any thoughts?

edit: I had a slam after we took over the pool in May after letting the FC drop below target a couple of times. I’ve kept doing the daily drop chlorine test ever since so I know where my numbers are.

 

[domct203]

Remember, algae spores (and bacteria) are microscopic. By the time you see green there are millions of them.

If you lost that much FC overnight, something is brewing alright. I would SLAM.

After completing the SLAM, try targeting 1 or 2 ppm higher for your daily target. My pool is under two large trees, and I get ‘organic matter’ in my pool constantly. I maintain 8-10% of my CYA as my daily target (SWG), otherwise I end up with a ‘dull’ looking pool and high FC demand.

Every pool is different, the trick is to learn your pool.

 

[Jimrahbe]

Jean,

What is your CYA? When was the last time you tested it?

Like Dom, I run my FC on the high side.

Thanks,

Jim R.

 

[Jean-ji]

It was 60 yesterday and I added stabilizer along with salt, which was 2700. CYA is still at 60, but it usually takes two days to come up. Of course I added it before a SLAM.

I was keeping my FC at 6, but with the rains it was down to 4.5 in the mornings this week and I added bleach to get it back to 6. I just added bleach to get it back to 6 and it did. Just in case my powder went bad overnight. Wishful thinking. I just added the rest for a SLAM and am heading off to Leslie’s to get bleach.

Interestingly there was another thread this week from someone north of here that runs his FC on the high side and he keeps beautiful records. He ran into the same thing: clear water but the chlorine being eaten for no discernible reason.

 

[Jimrahbe]

Jean,

On surface it does sound odd...

My theory is that you never really killed the algae from your original SLAM.. With a SWCG adding chlorine all the time, you were able to keep the algae under control. Then comes the storms and you adjusting the cell's output down, allowed the FC to go low enough for the algae to take control. At this point my theory is a good as everyone else's..

I would recommend that you do a SLAM at the 80 CYA shock level and do it a day longer than necessary and make sure you brush well, a couple of times a day.

Thanks,

Jim R.

 

[Jean-ji]

Thanks, It’s hard to believe alagae could live in 4 and 6 FC levels for three months. I’m a new pool owner though, so I honestly don’t know.

I added enough stabilizer to raise it to 70 yesterday, I take things up in increments so I don’t overshoot. I added enough chlorine to get to a 28 FC with a 70 CYA for the slam. I’ll start my checking and dosing every few hours. At least I’m catching it in the early stages.

 

[jimmythegreek]

Remember the higher the cya the more chlorine u need. Check ur PH is good and slam at current cya #s don't add more stabilizer til u get this under control w the slam then go up to whatever level but 70 is fine w swg

 

[Jean-ji]

I added the stabilizer the day before the FC tanked. CYA was 60 and I put in enough to bring it to 70.

I started the SLAM yesterday, checking and adding chlorine every two hours. I was losing 4 FC every two hours and then 2 FC in the last two tests before stopping for the night. This morning, I lost 5 overnight, so it’s improving. I’ll continue brushing, but there is nothing to see, it’s at the microscopic level. Water is clear and has been from the start.