Re: CO2 Regulators - The Sequel

> From: James Purchase <jpp at inforamp_net>
> Date: Thu, 05 Dec 1996 08:49:02 -0500
> It sounds sensible to me, but in an earlier post George Booth doesn't
> recommend turning a manually operated system off at night. George, is
> that because of the difficulty of fiddling with the valves or
> re-adjusting everything every day? I realize that with a manually
> controlled system I am going to have moderate (I hope) pH swings but
> several items in the archives state that this is not unduly stressful.

I think about it this way:

With a manual system, I would like to adjust the CO2 flow so that, on
average, the CO2 going into the tank just balances the CO2 used by the
plants and the CO2 diffusing into the atmosphere.  The plant use rate
will vary from day to night, of course, but the loss to the atmosphere
should be fairly constant.  The CO2 levels in a carefully balanced
system will then vary between high and low levels.  Hopefully, the low
level (when plants are photosynthesizing the hardest) will still be
high enough and the high levels will not too high.  In our manual
system, I think we saw a variance around 15 ppm; 12-20 or something
like that. 

There are two phases to CO2 injection: building up the concentration
and maintaining the concentration.  If you turn off the CO2 at night
and, even worse, turn on the airstones, you will drive the base CO2
concentration down to very low levels.  When the CO2 comes back on in
the morning, you would need to increase the injection rate so that the
concentration builds up to a good base level then cut it back to the
"balance" flow.  Probably no one is going to do a two stage thing, so
when the CO2 comes on it will be running too slowly to get the
concentration up to where the plants are going to do well.

And you will get much larger pH swings by turning it off at night than
you will if you let it run at a balance rate constantly.