I've used a controller for quite some time and they work pretty good as pH monitors... But you should only use the controller as a fail-safe in case of a CO² tank dump. Thus that it cuts the CO² off when it shoots down to a dangerous pH level. Then you still need a pretty accurate and stable regulator and needle valve to get to the required stable BPS to stay in the safe pH range.
In general consensus, it's said a dual-stage regulator also should prevent a tank dump, so everybody takes it for granted. But if you get to this point and it doesn't it'll be too late. And this point is reached at a near-empty CO² tank.
What I personally find questionable about permanent pH monitoring is, a pH meter is a voltage meter and via the probe, the tank water is constantly grounded to the electrical grid. And there will constantly flow an electrical current through the aquarium. All other electrical equipment in and around the aquarium also spreads an inductive current and every body of water has a capacitive property. A body of water in a glass tank that is insulated and not grounded will have no electrical current running through it. Once it is grounded it will have a current running through it. Depending on the severity of this current fish can be affected and irritated by it.
There is some controversy to it, in how far fish are affected and this is never fully scientifically investigated. Some say you always should ground the aquarium water for your own safety and therefore Titanium ground pins are available in the trade, others say you definitively should not for your fish safety and steer away from it.
I tend towards the group that steers away from it... Referring to an old school issue from back in the day where everybody used tube lights and Ballasts, it was said from experience never to switch on all lights at once because the sudden light flash startles and stresses the fish. But this theory didn't seem to be very true since lots of us use LED nowadays and switch on lights suddenly, some even use LED controllers to simulate Lightning effects and experience the fish are not at all startled by it. The conclusion you can take from this is, it wasn't the light but the sudden conductive or inductive electrical power surge from the ballasts, starters and tubes likely were the cause running back and forth through the aquarium water and moist air under the hood. After all, light is light, and it ain't the light thus it was something else startling the fish and electricity as a cause is the only thing that remains in this scenario
Anyway, long story short a permanent pH probe grounds the tank and runs an (unknown) voltage through the tank or else it can not measure anything. It also grounds the tank to make all other currents be it inductive or capacitive to run to the ground. In how far your fish will be affected and feel a constant sensation that shouldn't be there or not remains to be seen.
I only think you should know, have your thoughts and make your own decision about it. 🙂
I decided I had my fair share of CO² experiences, I liked it, but rather keep going low tech for the rest of my aquarium carrier, less hassle. And i do not ground my aquariums, I pull the power plugs before I stick my fingers in it for my own safety.
Btw if you are curious, get a multimeter and set it to measure voltage put the positive pin in the tank water and ground the negative pin. In 9 out of 10 aquariums you will measure a voltage, there are people that reported up to 60-volts others much less. In most cases, this is capacitive voltage. But this is the voltage that will run as a current to the ground if it is grounded.
