OK. I did another 55 gal change last night. Tested this morning and the nitrates are still off the chart.
I tested the fresh SW i added and there were no nitrates (yellow w/ API test).
I'm at a total loss here. Could there be something in my tank affecting the test results?
I've tested from the DT and the sump at different times with same results.
I will take to an LFS to compare, but any other ideas?