i got my z9 mini batch 2 running for few days @ default 550
has no problem at all so i decided to rise it up to 625
all good still
today for almost 12 hours i have run it at 650 freq

i just notice as i was checking on pool (suprnova)
i cant get 100% efficiency
i thought it was my internet line 
but all lines are good

i switched it back to 625, and observe
i have all running 100% at pool side

which make me made my final setup at 625
running 13-15K sols

temp
64-66 degrees