Help!! water parameters

I just started my tank 5 weeks ago. It cycled great all parameters were where they are suppose to be. So I drove an hour and a half to two stores in the QC and purchased 1 clown fish from each. Brought them home, and slowly acclimated them. Two days later I find my first one dead in the tank. At this time I chalked it up to possibly a sick fish from the beginning. Never ate any food and hid all the time. I immediately removed the body and did a small water change. It sux but these things happen in the hobby.
Two days later (today) I get home and find my Black snowflake clown dead in the rock work. After I lost the other one the snowflake started hiding and stopped eating. I tested my water parameters and the are spot on where they need to be.

PH 8.0
Ammonia 0 ppm
Nitrite 0 ppm
Nitrate 0 ppm

I'm at a loss here. Does someone have a more accurate test kit than the API marine test kit?