Water is balanced, FC is being used too fast


New member
Oct 16, 2017
Long Island, NY
Hi All,

This is my first post. This forum has been invaluable to me, and I am grateful for the community. I have truly learned a lot in the past three years on here, so thank you all.

My question-
I am pretty meticulous with balancing my water. I check the FC and PH every other day or so. Since opening the pool at the end of May, I have not let it drop below 4 ppm *(see below) and keep the PH between 7.6-7.8. It seems once a season my FC gets used up too quickly and the SWG can't keep up. I end up SLAMing the pool and after a couple of days, I pass the overnight test, CC is <.5, and the water is clear.

The thing is, my water is always clear when this happens and I have never let the FC drop below 4ppm. I noticed this beginning to happen on Saturday, June 29, and we had an intense storm pass through here on Sunday, the 30th. The day after the storm, I noticed the water was slightly cloudy, but I could still see the bottom clearly. I would have blamed the issue on the storm washing debris into the pool, but I noticed the FC was getting used quickly the day before when the * FC was down to 3ppm. I bumped the SWG up to raise the level back up, but it didn't seem to help. Could the fact that I let it drop to 3ppm the day before have caused an outbreak like this?

I cleaned the filter day before (Saturday, June 29) when I noticed the drop in FC just to try and help, so I don't think that's the issue. The pressure was just barely a PSI over from when I opened the pool. SWG cell looks good too.

I started the SLAM process yesterday and did not pass the overnight loss test.

My numbers prior to the SLAM were:
FC 3ppm
PH 7.5
TA 70
CH 160
CYA 60ish

I brought FC up to 24ppm, as per the chart, I realize my CYA isn't ideal.

Any idea on what I'm doing wrong or if I am missing something? I'm at a loss here. Thanks in advance.


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Welcome to the forum!
The pool system got overwhelmed in one part or another and algae took hold. You have responded appropriately by raising your FC to SLAM level. Now follow the SLAM Process. Test and add chlorine several times a day.

I would suggest in the future not keeping your FC so close to the minimum. Maintaining at least a 5 or 6 ppm FC gives you some cushion for those high load organic days that occur.