I bought a TF-100 kit to aid in my conversion from baquacil. I have a question about how to correctly measure the FC. Following the kit directions i added the scoop of R870 to the water sample and mixed it. The water turned bright pink. Per the directions I then added the R871 drops one at a time until the water turned clear. This is where my question comes in .... while the water turns clear, it does not stay clear long ... it goes back to a light pink. Do I calculate the FC based on when the water turned clear (even if it does not stay clear) or should I keep adding drops until the water turns clear and stays clear?