Let's revisit the LR
What "kind" of rock is it? Like Caribbean rock? River rock?
How long have you had the rock?
Where did it come from? (Possibly come from another reefer who lied or didn't disclose they used MEDS to treat the tank when they had the rock)
MY POINT: rocks can be very porous and hold onto past medications or other foreign substances
River rock could have various minerals embedded in them that a test may not detect. Like a rock that's Limestone
I used 100% Caribsea Life Rock, I believe 80lbs. The rock was new and not used in any other tanks. This is the rock that was originally cycled with the tank, so the rocks have been in the water for about 2 years now. No harsh medication has ever been used in the tank (I used a single bottle of Microbacter 7 and a single bottle of vibrant at some point over those two years).