Just thought I'd mention that although it may be necessary to get more aggressive, I noticed a simple rinse in hot water was all that my color test blocks needed to clear up. I do all my testing outside, and my blocks are just rinsed in pool water. Over time they've gotten a little cloudy, but after cleaning up from a small fire I had in my pump room, I brought the test blocks inside and rinsed them in hot water. Seemed to have improved their clarity a bunch.