You may be over-thinking this. I do not recall seeing any complaints about high-quality solenoids freezing open, although it is possible. Your relayed timers would certainly address some of the backup issues. However, if a timer fails in the “on” position, then you are down to the one-timer-only mode anyway, and may not be aware of it, unless you intend to verify operation regularly ...but then there’s that nagging Murphy’s law about “If it can wrong, it will.”
A dual stage (not gauge) regulator should prevent an EOTD event, if that is a concern and they do provide, generally, that increased backup-in-depth aspect.
You can also run CO2 24/7 (I do) and do it without any problem. In fact, I believe it to be beneficial and it actually reduces overall CO2 consumption.
Maintaining good gas exchange is always important regardless of CO2 overdosing concerns, but it should be done via surface agitation and airstones aren’t that effective at doing so. Better to use a pump or skimmer.
I was thinking of using two timers in serial, one timer backs up the other. Both have to be on for CO2 to be on. I have the CO2Art regulator which is a dual stage. I have seen people post that their regulator "got stuck" but I'm guessing a very rare occurance.
I have to missing something, I didn't think it was possible to run CO2 24/7 with animals in the tank! I assumed once lights are out, with CO2 running they are asphyxiated within hours due to build up of CO2, which is why I am so concerned about having a lot of safeties in place. Same with if lights don't come on and CO2 does. I'm assuming at 30ppm, your tank animals are one minor "oops" away from a tank kill since people note that a little higher and their fish have trouble breathing.
24/7 would waste gas, but one side benefit is it avoids the daily pH swing which I know people say doesn't bother their animals but I am skeptical its a healthy thing. 1 pH drop/rise is a 10x increase/decrease in acidity. Good food for though although I need to understand CO2 levels a little more.
Originally Posted by Blue Ridge Reef
Besides a pH controller, I use a Kasa smart strip that runs a powerful air pump for the last 10 minutes each hour, and then all night while the CO2 is off. Only set them up this way in January but it's worked for me without a hitch so far.
That's an interesting idea. Does it expel all the CO2 gas in that 10 minutes and create a pH swing every hour?
Not sure where you heard this, but good quality CO2 controllers like Milwaukee and American Pinpoint Marine are rock solid.
I've used one full time during the CO2 period for years. IMO, makes it easier to dial in CO2, and acts as a fail safe protecting fish. With a tank full of mature and hard to replace Rainbow fish, that means a lot to me.
That's good to know they are reliable! A couple articles I read indicated they end up switching on an off too rapidly. My experience with pH probes in a lab and with owning a Hanna I was using for hydroponics is the pH probe is the weak point and needs to be well maintained and calibrated, replaced every so often. I remember in the lab seeing them "drift" when they started to go bad. Of course part of the issue is taking them out of the solution and letting them dry, that's what kills them early so maybe sitting in the aquarium water full time keeps them accurate and functional.
Also I am using lots of Seiryu stone and have noticed a KH drift from 4dKH to 7dKH within 4 days. So per another poster's comment, I wonder how that weekly drift would play on a pH controller.