correct FC measurement using TF-100


LifeTime Supporter
May 31, 2010
I bought a TF-100 kit to aid in my conversion from baquacil. I have a question about how to correctly measure the FC. Following the kit directions i added the scoop of R870 to the water sample and mixed it. The water turned bright pink. Per the directions I then added the R871 drops one at a time until the water turned clear. This is where my question comes in .... while the water turns clear, it does not stay clear long ... it goes back to a light pink. Do I calculate the FC based on when the water turned clear (even if it does not stay clear) or should I keep adding drops until the water turns clear and stays clear?


TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
SWSuburban Chicago, IL
You keep counting drops till the water stays clear. So if it's only like 10 seconds and turning pink again, add another drop and count it. You want the water to stay clear for a good 30 seconds. :)
Welcome to the forum! :wave:


LifeTime Supporter
Nov 18, 2009
Sacramento, CA
If it immediately goes back to pink than you are not done, and add another drop.

If it stays clear for a while, but goes back to pink after 30 seconds or so then you are done.

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