You only really need the ORP probe if you are going to run Ozone. The probe will control your ozone generator so that you can set up a parameter and have the Apex keep the reading steady. Also you only really need 2 pH probes if you are running a Calcium reactor. 1 probe for tank pH and one for reactor effluent pH. Same thing as the ozone, the apex will control the co2 solenoid based on the effluent pH you set it up for. The only other thing i would suggest getting is called the breakout box. You can hook up 6 electronic float valves or water sensors. Good for controlling ATO, sump levels, flood detection, RODI, etc. I am going to try to pick one up for my Apex along with another EB8 as I have found I ran out of outlets.
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