Yeah if you have good plant growth and minimal algae, no need to change your setup. A solenoid makes things easier if you need to crank up the CO2 for algae issues. You can crank it up during the lighting period with worrying about gasing your fish if, you turn it off when the lights are out. Increasing surface movement at night would make things even safer.
When your CO2 cylinders get closer to empty, do you notice any increase in bubble rate and or CO2 saturation?
As far as the tank being completely empty, I haven't experienced that yet. When the gauge is a half way from 100 psi to 0 psi, I just go ahead and refill. I haven't noticed any increase in bubble rate or Co2 Saturation. It's always been constant with me. I could let it run all the way to empty and see what happens, but that's in about 5-6 months lol.
Anyone know if Walmart sells CO2 paintball tanks and valves?
When looking for Co2 tank before I start injecting Co2 into my tanks, I did a few looking around and Wal-mart only carries 16oz Paintball Co2 Tank. 100% sure they don't carry and vavles for it.