Specific Question Regarding TFP CH Test...

#1
Greetings all:

While doing my CH testing, I'm getting wildly different results based on whether or not I stir my sample during the the last step of the testing.

The instructions say: "Add R-0012 one drop at a time until the color changes to blue. Multiply the number of drops x 25" My question is, should I be stirring my sample (either constantly, or after each drop) while adding the R-0012 reagent?

If I DO stir, I'm getting a CH reading of around 175 PPM. If I don't stir, it's closer to 375 PPM - quite the disparity in results...and one that could potentially have me make a significant error regarding chem additions.

So....to stir, or not to stir...?

Any and all help would be appreciated!
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
14,647
Tucson, AZ
#3
Get a SpeedStir, it's the best way to do testing.

Yes, you need to continuously agitate the solution by stirring. Few people have the skill to swirl with one hand while adding titrant with the other, so getting a SpeedStir improves the testing greatly.

Also, make sure you are reaching the proper endpoint. The test ends when the blue color stops getting more blue, NOT when you first see the blue color. This is typically 2-3 drops beyond when you first notice the blue color. Many people make the mistake of ending the test at the first sight of blue and that leads to variations in drop count.
 
OP
OP
D
Apr 29, 2017
8
OC, California
#4
Constant stirring.

I do mine with the speedstir. When I switched from manual swirling to speedstir, my CH value dropped 1/3!

A speedstir would make a wonderful Father's Day gift ;)
Thanks for the fast reply!

A speedstir is exactly what I use...which, unfortunately, leads to more confusion for me. I just looked at my Municipal Water District's annual water quality report for 2015 (2016 hasn't been issued, yet) and it says that the CaCO3 levels here (Orange County, CA) should be around 330 PPM.

So...what gives? Bad reagent?

I'm setting up a new SWG - I'm trying to dial this thing in before turning it on and this is vexing me....

- - - Updated - - -

Get a SpeedStir, it's the best way to do testing.

Yes, you need to continuously agitate the solution by stirring. Few people have the skill to swirl with one hand while adding titrant with the other, so getting a SpeedStir improves the testing greatly.

Also, make sure you are reaching the proper endpoint. The test ends when the blue color stops getting more blue, NOT when you first see the blue color. This is typically 2-3 drops beyond when you first notice the blue color. Many people make the mistake of ending the test at the first sight of blue and that leads to variations in drop count.
AHHHHHHH....THAT may be the ticket.

Off to test again!!!
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,330
San Dimas, CA (LA County)
#5
Trust your testing. Water quality can vary throughout the year depending on the source. If right now they're pulling a lot of snowmelt from rivers and reservoirs, it's going to be softer than if it was pumped from a well.
 
OP
OP
D
Apr 29, 2017
8
OC, California
#6
Get a SpeedStir, it's the best way to do testing.

Yes, you need to continuously agitate the solution by stirring. Few people have the skill to swirl with one hand while adding titrant with the other, so getting a SpeedStir improves the testing greatly.

Also, make sure you are reaching the proper endpoint. The test ends when the blue color stops getting more blue, NOT when you first see the blue color. This is typically 2-3 drops beyond when you first notice the blue color. Many people make the mistake of ending the test at the first sight of blue and that leads to variations in drop count.
Yep. That was it. I'm now getting repeatable results right at 350 PPM - right in line with what I'd expect them to be, given my experience with water hardness in Orange County.

I'm really glad I asked. I can't even find calcium chloride here - when I asked the guy in the pool/garden section of Home Depot, he said, "wait, you want to ADD hardness to your water?" That gave me enough pause to go back, retest, and ask for help!

Anyway.

Thanks a ton to both JoyfulNoise and Richard320 for your help!!!