Anyone use fmu with OPKs?

Kimberly

All of my lines are barely visible, but it's still early (CD9). I stay really hydrated, completely clear pee all day and struggle to do a 2-4 hour hold even when I stop drinking. I'm worried about missing a surge because my urine is too diluted. Would using FMU cause an issue or false positive? My box only says 10am-8pm but doesn't say anything about fmu.