Dang...

The one unfortunate downside to the Horiba LAQUAtwin probes is that being Ion Specific Electrodes, they are fine tuned to measure Calcium, Potassium and Sodium in the relative absence of other ions. This means that the LAQUAtwin probes do encounter interference from other ions, as in the LAQUAtwin Calcium probe is affected by magnesium levels above 1000ppm, which wouldn’t work well for reef aquarium use.