Based on your description, it sounds like you might subtract 10ppm when you do your CYA test.
Yes it can test higher levels, but may bleach out so if you see a quick pink flash then add more DPD powder until the pink/red stays. Then, titrate as normal. This is described here as follows:schrody said:One question: The book that came with the K-2006 says the FC test is only good to 20 ppm. From the collective experience on here is it accurate to higher levels?
duraleigh said:I see only benefit in increasing you pump even more. You have a filter capacity of 60 GPM so I think running your pump around 45gpm or so would be ideal.