Quote Originally Posted by waterbear View Post
....If you are having trouble seeing the color change then add a few more drops of the indicator solution to your sample or try using a 10 ml sample where each drop is 25 ppm CH. TO do so you would add 10 drops of calcium buffer to the 10 ml sample, 3 drops of indicator, and then titrate.
If your color changes to a blue color that reverts to purple (fanding endpoint) you probably have metals in the water (a common interference). If the color has changed from pink to purple then you have not finsihed the titiration and reached the blue endpoint. Remember, if you have high calcium hardness and are using a 25 ml sample size it can take 20, 30, 40, 50, 60, or even more drops of titrant to see the color change to a blue.
Thanks Evan. I see you edited your post (thanks for the clarification) while I was out back trying your suggestion using a 10ml sample. I also used a second tube for reference/comparison (without adding tritate). While the starting color was darker than my original attempt, I still couldn't see the change to blue even after 20 drops of tritate; the two tubes still looked the same to me (since I don't add calcium, I strongly suspect my calcium level wouldn't be that high, ie - 20 drops in 10ml sample = 500ppm). Out of curiosity, I added a couple drops of indicator to each tube to darken the color more, and this time I could see a difference; while subtle, the tube with the tritate added looked blue compared to the tube without tritate (yea!). It seems I can see the difference easier if the color is much more saturated.

So this is what I tried;

1. 10ml water sample in each tube
2. Add 10 drops of buffer to each tube
3. Add 5 drops of indicator to each tube (6 drops helped even more, is this OK?)
4. Add tritate drop by drop to #2 tube only (using #1 tube for reference/comparison)

Doing it this way, although still kind of subtle (I guess my color vision ain't so hot) it looked like the pictures on the link you provided. I could see my #2 tube certainly looked blue after 10 drops (adding 1 or 2 more drops didn't change this so I figured I was at the endpoint) giving me a reading of 250ppm at most.

Would this method give me a good result? Or does adding the extra indicator throw off the results?

Thanks again.