Copper getting passed my 7 stage?

[RMS18]

I used my Hanna copper checker to test my DT tank. 2 weeks ago I added fish back in who were in qt with copper. When I added them back in copper in the qt was reading .5ppm about. I netted the fish as to not add qt water into the dt. Since then some acros are bleaching at tips and or base. I thought it was from po4 swings and a slight alk swing since adding fish back. Then I tested the DT water and the Hanna copper checker read .02, I tested again and it read 0.0. I tested my fresh made sw and that tested at .05ppm. All resin, carbon and filters are new in the rodi. I am waiting for a icp test to arrive.

Could this be the margin of error for Hanna test kit, or do I have copper In the DT and rodi?

 

[Randy Holmes-Farley]

it is unreliable at low levels. Almost certainly you have none. many folks see this fault and do not find copper with a better test, icp.

 

[RMS18]

it is unreliable at low levels. Almost certainly you have none. many folks see this fault and do not find copper with a better test, icp.

Thanks!