Things you could take into consideration about aquariums and electricity and Ph meters/controllers.
An aquarium simply is a bucket of conductive water, the solids (salts) in this water determine its conductive capacity. When the waterbody is grounded it will conduct, when it's not grounded it will charge with electrons capacitively.
It requires electrical thus conductive equipment, such as pumps, heaters, light, optional feeders and or measure equipment. This equipment runs power 24/7 over coils and such back and forth from and to the electrical grid and it creates a magnetic force field, the device itself and the power cable has it. In simple terms, this forcefield is an electron flow over the atmosphere and your aquarium stands in a magnetic electron bubble. Therefore a capacitive and or conductive coupling between equipment and aquarium is unavoidable.
This actually also happens in your home installation, if for example there are several electrical cables in 1 tube in the wall and 2 cables run power and the others are switched off. Then there still is a conductive coupling between all cables because of the forcefield from the cables that run power. In some cases, people report LED lights that keep glowing faintly when actually switched off? This phenomenon can be is caused by such a conductive coupling from the cables in the wall. Look up both types of couplings to learn a bit more about how and why it establishes.
Back to the tank and its capacitive properties and the capacitive coupling when all equipment is switched on... As said it's a bucket of water in glass insulation and as long as the water is not grounded it can only charge till a certain point and only release this charge again over the atmosphere (moist conductive air). And these values are harmlessly tiny. This all changes when you ground the water, this you can do by sticking a finger in the water and touching something conductive such as a heater pipe from the house. In some cases, you can feel it. You can also take a multimeter and set it to measure (small) voltages, put the positive lead in the tank water and hold to negative lead to something grounded and you'll have a 99% chance you will measure a voltage. Reports of people measuring up to 60 volts from their aquarium can be found out there...
And as said, when you stop measuring and stop grounding the water then it just remains a charge the water holds and it goes nowhere. It only conducts physically when grounded.
Now the Ph controller is a voltage meter, it measures the difference between the fluid in the probe and the water to determine a value that is recalculated to a pH value on the display. And it only can do this when connected to the power grid, thus the Ph probe grounds the water. Depending on the conductive coupling capacity and the capacitive coupling capacity between other equipment and the water all this charge will leave the tank over the pH probe. And since the pH meter is a voltmeter this electricity flow can cause incorrect and fluctuating measurements. Then your pH controller renders rather useless and unpredictable. It doesn't need to be much, you can find reports of people complaining about Milwaukee controllers with a constantly rattling relay and solenoid. Simply because of the 0.1 pH threshold and a fluctuating measurement because of the electrical interference in between its set threshold value making it switch on and off constantly. This could happen suddenly when the heater switches on or off and the conductive coupling it causes alters.
Some Milwaukee controllers use a low reference voltage and could be more susceptible to interference than other brand controllers using a higher reference voltage, some brands such as Hanna equip their meters with a separate ground pin to circumvent these interferences and guarantee more stability. I've used the sensitive Milwaukee for quite some time that rattled now and then and also used the rock steady Hanna, but the Hanna I could feel measuring with my finger in the water.
Anyway, stable or not, that's not my point, the point is a permanently connected pH probe will ground your aquarium and make it conductive.
An old school rule of thumb was never to ground your aquarium water... Simply pull all the plugs of electrical equipment before you are thinking of sticking a finger in it. Not only for the latter but also and maybe even more for your
fish's LLO function.
If we can measure it and in some cases even feel it, then what about the fish? This debate still holds a lot of controversies, which we yet don't fully understand. But there are reports of claims that electrical current flowing through the water can cause harm to fish but yet there is no real scientific proof of at what values it starts and ends. Well, it definitively ends at the high voltages that we know. But a constant long term irritation in the lower range is still beyond our grasp, we can't tell and the fish can't tell us. It's the lack of proof overshadowing the plausibility the trade uses to sell to you for your convenience.
I can only give an opinion, which is irrelevant at this point...