What Nitrate level are you getting? This is testing the newly mixed salt water, right?
What is the TDS(total dissolved solids) of the purified water? The TDS reading is the way we know if the water purification unit is working correctly.
I would be happy to test the TDS for you. Bring your water over to me in Murray. Call/text me at 808-345-1049
Even with straight tap water, after it goes into the aquarium, the biofiltration should reduce the Nitrate to an acceptable level. What is the Nitrate level of the aquarium water?
Aloha,
Mark

808-345-1049
750 E. Lakepoint Dr. #4V in Murray