How to read meniscus on TF-100 test kit.


Well-known member
May 29, 2017
Worcester, MA
Hi Folks:

I've been using my TF-100 test kit for a week or so now and have just finished a SLAM. I've got a SWG pool with CYA of 80, which means my target FC for SLAM is 31, which is high.

Anyway, the TF-100 requires 10ml of pool water to do the FC test. You pour the pool water into a dedicated graduated cylinder up to the 10ml mark.

My question is....where to you measure the 10ml from? I've always learned that you measure from the bottom of the meniscus (ie meniscus lowest edge should be at 10ml mark).

The meniscus of the water is quite large and I find my FC readings can vary considerably depending on where I put the meniscus. If bottom of meniscus is at 10ml mark I can get a FC reading of 34ppm. If I measure from top of meniscus (slightly less water) I get 31 ppm.

Where do you guys put the meniscus when measuring?


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Bottom. That is the standard chemistry method to my knowledge. It has been 38 years since I took any chemistry classes though ------

Take care!


Gold Supporter
Silver Supporter
Aug 14, 2016
Rochester, NY
I was always taught that the lowest point of the meniscus is what should be at your desired measurement point.

I assume that all chemical measuring cylinders are still calibrated to this method.