programming solenoid for CO2 dosing

[Xerses24]

I have a solenoid that i'm using to control my CO2 dosing in a freshwater tank. I want to keep the pH of the tank at 7.3 using the solenoid. Here is my current code:

Fallback OFF
Set OFF
If pH > 7.30 Then ON
If Time 20:00 to 07:00 Then OFF



The problem I am having is that there is a delay between the CO2 turning on and the pH probe picking up the change in pH in my sump. For instance if the pH is 7.3 the solenoid opens, but it takes the probe ~3 minutes to drop below 7.3. By that time there has been too much CO2 dosed and the pH drops all the way down to 7.1 over the next 4-5 minutes even after the solenoid is closed.

I am looking for a way for it to turn on when the pH gets above 7.3, dose for 2 minutes, stop dosing for 3 minutes to wait for the probe to get a reading and then repeat as necessary. Can someone help me figure that one out? Or if there is another more elegant way i'm not aware of, obviously that would work too. I guess what i'm looking for is a MAX time instead of a min time.

[RussM]

That fast of a drop indicates that you are allowing too much CO2 in too fast. You should dial down the rate of CO2 using your regulator.

But for for a purely programming solution, try this:

Fallback OFF
OSC 0:00/1:00/4:00 Then ON
If pH < 7.30 Then OFF

[Xerses24]

Thanks, that should work. I took your advice and am trying to dial down the CO2 to just the right level. It has helped a lot, i'm hopeful I can get all the way there just doing that.

[margan]

Dailing down the CO2 should reduce wasting CO2 and save you money too! It worked for me, tripplling how time between refills.