My first SLAM. What to do if it rains mid SLAM?


May 24, 2019
I started my first SLAM yesterday. CYA 45 indicated a SLAM level of 18 for FC.

Right before bed, I tested FC and got a reading of 20.

I woke up before sunrise today to test and read 17, or a loss of 3ppm. I added more chlorine to get it back above 18. The pool has cleared up a lot and I gave it another good brushing, getting rid of nearly all remaining visible algae.

I need to keep SLAMing but now rain showed up in the forecast for today. Do I need to preempt the rain with additional chlorine? Or just keep the process as normal and add chlorine as the rain dilutes throughout the day.

Any tips for SLAMing through rain would be appreciated!


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Rain has little effect on the SLAM process other than you getting wet adding liquid chlorine!

Would be best to round up your CYA to 50 and use 20 ppm FC.


Gold Supporter
Jun 28, 2017
Fresno, CA
The goal is to keep your FC levels at SLAM levels so test and stay the course. Remove any debris that may find it's way into your pool and brush the pool surface when you can.


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
Rain won't do much unless it comes down so hard the pool starts overflowing.

If your pool is 48" deep, an inch of rain is only 2%. You won't be able to measure that small a difference on any of the tests.

The gloomy skies work to your advantage. It cuts the chlorine losses to UV from sunlight.