TF100, calcium test, sample size?


Jun 12, 2019
Phoenix, AZ
Just getting into the TF100 kit I recently ordered & was doing the calcium test today. The card said to fill to the 10 mark but I saw a video on YouTube where they fill to 25? Reason I ask is because after testing at 10, the red/pink color never seemed to definitively turn blue, just noticed a lot of floating red/pink particles with just the slightest hint of violet. I live in Phoenix & the water here is real hard, just wondering if I’m doing this test right? I’ve got the Speedstir, will use that next time. Thanks again


Gold Supporter
LifeTime Supporter
Jul 16, 2010
Portland, Oregon
Follow the TFTestkits card. Use your speedstir.

If your water is hard, expect it to be hard in the testing. Look for the actual change in color.


TFP Expert
LifeTime Supporter
Jul 21, 2011
Eastern Ohio
Both sets of instructions will work. Using the 25ml was the standard when the videos were created and offers the highest level of accuracy. That said, accuracy isn’t nearly as vital in CH as it is in other tests so in order to save the end user some reagent the instructions were altered to use the 10ml. This is also rather accurate, just not as accurate as using the 25ml.


Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
I first started to do these tests using the 25cc sample of water. I can't do anything but that now.. You learn something for the first time and its hard to change, right? if I tried to remember do use 10cc instead I'd mess it up cause I can't remember the formula! But I can do the 25cc one time and again and never need to review the instructions.

I'm just a 25cc girl :thequeen:

Maddie :flower: