Twice today I have added the scoop of powder to the 10ml of pool water to perform the chlorine drop test and it has not changed color. I went and got a new sample the first time and a scoop changed color. The second time a new sample did not change anything so I added a second scoop and it changed. I know there is high levels of chlorine in the sample as I am currently shocking. Any idea what is going on and is adding a second scoop theright thing to do?