I'm using American Marine controllers on three of my tanks and after about a year the probes start to register changes slower as the globes become contaminated with mineral deposits. When calibrating (checked every 4 months at my house) if a probe takes too long to settle when going between reference solutions I change it out.any reason for this? maybe they get dirty/corroded when submerged?
The reason I say "at this time" is because it's necessary to get a better understanding of CO2. It's not impossible to use the controller, only that the CO2/KH/pH relationship that the controller tries to use is broken in tank water, and adjustments need to be made. Other acids affect the reading and the result is a surge of gas then a curtailment. This cyclic behaviour of CO2 injection causes concentration level instability which gives rise to some forms of algae. It's better to learn how to inject gas in a stable manner before using the controlling function of the meter. Neither fish nor plant care about pH stability, and pH stability comes at the cost of CO2 stability which you clearly can see affects fish and plants alike.
There's a particularly massive one which layed out all the science with for and against but I can't find the things anywhere.The pH/KH/CO2 relationship in a tank is nonexistent. The reason for this is that there are other acids in the tank water which are not related to the Carbonic acid being produced by the CO2. Your pH controller has no idea where the pH reading is coming from and it cannot separate pH effects of the Carbonic acid from the effects of these other acids so in effect it is constantly reading a false high CO2 concentration level. You yourself reported that the dropchecker revealed that the CO2 level was lower than previously thought. This should have been an indication that the controller has no idea about CO2 levels because the one-and-only parameter it uses to determine CO2 levels is corrupt. The tank produces nitric acid, phosphoric acid and may other types of organic acids naturally and these acids destroy any fidelity of the pH reading. This is precisely why we use an uncontaminated sample of distilled water adjusted to a known KH value in the dropchecker - to isolate it from the tank water, so that it's pH reading can only be attributable to Carbonic acid and not other acids.
If you believe nothing else, believe that algae cannot be starved. Plants require about 1000X more nutrients than algae so there is no conceivable way of starving algae without first annihilating the plants.
Remember that not only does the CO2 concentration level have to be adequate, but the concentration levels must be stable as well. If the concentration level fluctuates too much this affects the plants ability to use the CO2 and algae is then induced. Stable pH has absolutely nothing to do with stable CO2. Your best bet is to forget about pH because neither plants nor fish care about pH or pH stability. Worry more about stable and adequate CO2 injection rates and good flow. This is why a simple ON/OFF schedule for the solenoid will work better for you. Pick an injection rate, turn the gas ON 2 hours before the lights go on and turn the gas OFF two hours before the lights go off. When lights go on dropchecker should be lime green or yellow (depending on your flow and distribution).
Simplify you life by forgetting about bogwood, forgetting about pH, forgetting about KH and just concentrate on making sure that you have a stable and decent injection rate while not gassing the fish.
The probe has a membrane that degrades or mineralizes over time.any reason for this? maybe they get dirty/corroded when submerged?
That's why I use my controller to control a ph swing of .5 to 1.0. The solenoid is on a timer. I use a drop checker as well and put it in different spots in the tank. I use the ph of the tank in the morning as a baseline to go from. I feel that the controller gets the tank to 30 ppm as quick as is safe and does not waste CO2. I have a sump and need to run a pretty high bubble rate so I feel it helps to do it safely.We seem to hold this debate about every two months, and I doubt if any of us ever change our mind, but the debate is always interesting.
It isn't true that a controller can be set for a target pH and left alone to do the work for you. The reason is that as the plants grow the amount of CO2 needed will go up, requiring adjusting the target pH. As the water parameters change, such as with tannins, slowly dissolving carbonates, carbonate eating plants, etc. the pH will change independent from the ppm of CO2 in the water, so the target pH will have to change to keep the same amount of CO2 in the water. I think you have to accept that tweaking either the needle valve or the controller setting will always be desirable. You do get to choose which one you want to tweak though.