Hmm, I'd say you have a little bio-chemical war fare going on in your tank. When corals are iritate by another critter, coral, softy, fish etc. they release chemicals into the water column to drive off or kill the other beasty . In the ocean that's usally not an issue due to amount of water in your tank well.... I'd increase my water changes and run some activated carbon in your sump. I'd also probably take some water to a reefer friend or to the local fish store for a second opinion on the test kit.
hth
chris