Setting up my first reef tank and setup the APEX the other night. I have a 120 tank and about a 40 gallon capacity sump, sump has about 20 gallons in use so about 140 gallons of saltwater in the system. I ran the calibration for the conductivity probe and calibration kept failing. Finally went through on the 4th or 5th try.
I started adding rodi water to the tank and mixed the salt in the empty tank and did not yet circulate with the sump rodi water. I didn't go for the full amount of salt needed, I didn't want to over mix/add too much salt. I got it top where I figured I would be close to 30 ppt once I mixed the sump rodi water with the tank water.
Started circulating water and the probe read 6. I let that go 24 hours and it stayed there at 6. I figured there was probably a bubble in the probe, so shook the probe, bubbles came out and now it is reading 50 and has stayed there for 16 hours. I took a reading on the refractometer and it is at about 28. The refractometer was a relatively cheap $24 item on Amazon, I am assuming it is not a great piece of hardware but should be fairly accurate out of the box ....but I could be wrong. I figure I need to re-calibrate the conductivity probe. Yes?
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