As the water has gotten colder around here, I've noticed something weird when I do a FC test - particularly in a pool with a higher FC level (5+)...
The sample doesn't go "pink" as fast, so I wait... then after I drop-test the water goes clear. Then, 30 seconds later, it is a light pink... again. Add a drop or two of test solution, goes clear right away and then (depending on FC), goes light pink again.
Anyone else seen this?