[miata]

Hope someone can help soon. I just calibrated my MI pH monitor/controller SMS122 for the first time. I just be doing something wrong because when I put the electrode into the 7.0 solution I was able to Adjust the offset calibration trimmer (on the front) to 7.0, however, when I put the electrode into the 4.0 solution I was not able to adjust the SLOPE calibration trimmer (on the rear) to display 4.0pH, the lowest I could adjust it to was 5.8 (instruction sheet said I could adjust it to 4. After trying for over an hour I decided to put the electrode into my newly planted tank with pressurized Co2 to see what would happen. I put my Setpoint at 7.0 but since the pH was 6.8 the solenoied needle valve did not open. To get it to open I tried raising my set point above 7.0...nothing, I then lowered my set point to 5.8 & the solenoid needle valve opened. It is my understanding that the valve should open when pH reaches 7.0 & stay open until it lowers to pH to an acceptable level (which I don't know what that level is). Going from a range of 7.0 to 5.8 doesn't seem like it would be healthy for the fish (which I haven't added yet). Can someone please tell me what I'm doing wrong or misunderstanding? Thanks for any help you can give me.