Is there a purpose to have a conductivity probe and ORP?

[iridude]

I am about to buy a GHL Controller and looking at 4e and of course the 4. Before I take the plunge what is purpose of using a conductivity probe when you can check with a refractometer? ORP should be monitored if your using ozone am I correct? The only issue I have with GHL only has 6 outlets may need more.

[iridude]

That is why I am leaning towards 4e.. However, maybe I am missing something not getting the ORP and Conductivity probe.

[Member No. 1]

I have a P4 and use all the probes.
But to answer your question, you only need the basic two, Temp & pH.

I don't use the conductivity for controlling the salinity in my tank, but I do
use it to track trends and as a safeguard in case the ATO sticks ON and dumps to in much RO/DI, which would cause the salinity to drop. In this case I can turn OFF the ATO and get an alarm.

Since I use O3, I use the ORP for control. But even if I didn't, I would track trends to see if the water quality is decreasing. For example a decrease could be cause by a dead and decaying fish that was undetected.

If you go with the P4 vs the P4e, even if you don't use all 4 probes, you will still have the option to use the ORP port to add a second pH probe if you were to ever add a CaRX.