By the way Ph controlers?
Have one major disadvantage
Since they are permanently hooked to the power grit, they function as a ground pin, grounding the aqaurium water volume. SInce an aqaurium actualy is an electrical entity on it;s own, it should never be grounded. If it is and you have capacitive ot inductive stray voltage, than there will constantly be a current flowing through the water, with the possibilty it is causing irritative sensation to your lifestock. Than if you put such a device permanently in your tank water, make sure there is no significant stray voltage. As said an aqaurium is an electrical entity on it's own, there always will be milivoltage to measure. Ar eyou over millivoltage there likely is a stray, directly, capacitive or inductive. Not grounding the water it will do non at all, with ground it'll flow current and there shouldn't be.
Than if you use one still, because you are 100% sure you aint got stray voltage, than consider a Ph probe is a volt meter, it sends a current into the water and that way it measures the resistance between tank water and internal fluid as a reference for determine Ph value. Depending on how much voltage the device uses which is different by make depending on the electronics used behind the probe. Anyway very close to the pH probe there also can be a current in the water cuasing sensation to lifestock. Than if you use one, best practice is not to put it in the aqaurium itself, preferably in line or in the sump.
Then it's current will be not in the aqaurium itself.
When it comes to CO² and pH controlers there is quite some general consensus around about it that completely defies logic in the way it is explained.
Let me explain as far as my logic allows.
From our general experience, it is said we should have a stable CO² administering to the aqaurium to keep plants healthy and not favor algae growth. Thus we should have a stable BPM all through the light periode.
But with keeping plant metabolism into respect a stable bpm doesn't stand for a stable CO² contents in the tank on the contrary. Example, if we start with 10 bpm 1 hour before lights on and stay at 10 bpm for the rest of the day. And lights go on, the plant needs an x amount of time to metabolize available co² at 100% capacity. Lets use some logic here, then there should be more co² in the water all that time the plant is not taking up at 100% capacity. If bpm stays unchanged during the light cycle, there definitively should be a pH swing peaking at the plants highest uptake capacity. Conclusion, a stable bpm is not a stable co2 contents in the water.
Now if you use a pH controller wrongly, with controling the pH drop to make it shut down the co². Than actualy you could say the waters co2 contents is more stable. But not it's administering!! Because at peak plant uptake it adds extra on top, peak uptake makes to pH go up and the controler takes it down again with adding extra co². It is actualy oversaturating the water column with co² like that. Likely favoring algae growth and wasting co2 on top.
Than if you still decide to use a pH controler for your peace of mind, Than you still should use a drop cheker and a stable bpm.. Than firstly monitor your ph profile without controlling it via ph controller. And set the controller to shut off slightly above the peak value of plant uptake. That way you still have a stable administering via bpm and the controler will not interfere and never shut down the co² because it never reaches its set value if your bpm is stable. But you still have the safety it able to prevent a tank dump if it comes to that and you still have a permanent device to read your ph profile on the fly.
Not going to debate in how far this is usefull or not.. That's something personal.
If we would throw out everthing we don't realy need in life?? I guess we all would have a rather big pile of trash worth quite some cash in front of our doorstep.
Anyway, ph controler
Just know what it is,
Know what it does,
Know how to install it,
And know how to use it.
And not much can go wrong if you like a gadget like that.
There aint nothing realy 100% foolproof, if it never happened to you doesn't mean it can't happen to someone else. 