par metre not mesuring 10 wat led chips

[Coral Hoarder]

so i borowed a par metre off a friend and it doesnt seem to be mesuring corectly at 100% power to the fixture 5 10 wat chips 3 blue 2 white x 2 pendants the par in the tank on the botom says 20 now that inposible as i can bleach corals at 70% any one have and advice here ?

i mesured my ever grow fixture and redings were acurate so its not the metre

the only thing i can think of is the fuxture not being full spec and there for not mesuring proporly ?
i only have one kind of white led and one kind of blue led in it but it seems to grow corals well