The speedstir vial is thicker plastic which could be why the line is different. The TFP vials work fine with the speedstir. Usually this applies to the TA reagents, but try wiping the tip of the bottle between drops with a clean dampened cloth. Static electricity can cause the drop amounts to be different.
I don't test for CH often (or ever really) because it's very very low and I have a vinyl pool, but I believe you're supposed to use the 25ml volume for the CH test, not 10ml.
Also, make sure to tip the bottle fully vertical while dropping.
Alternately, pick a vial and use that one consistently.
I don't test for CH often (or ever really) because it's very very low and I have a vinyl pool, but I believe you're supposed to use the 25ml volume for the CH test, not 10ml.
Also, make sure to tip the bottle fully vertical while dropping.
Alternately, pick a vial and use that one consistently.