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more CO2 regulators

Hello all,

Forgive me for adding to this thread, but I feel compelled to add a comment.

It seems to me that a pH controller is a REQUIREMENT for any CO2 system to 
function reasonably.  As long as the water has a reasonably stable kH, a pH 
controller will maintain constant CO2 levels.  Such a system contains 
feedback, and forms a "closed loop" control system.  Closed loop control 
systems essentially compensate for drifts/inaccuracies of any component in 
the system, including the "plant" (the aquarium water in this 
case).  Without a pH controller, the system is "open loop", and one must 
try to adjust the flow rate (splitting hairs) to keep the CO2 (or pH) constant.

At my laboratory, we run gas lasers (including CO2!) and low pressure 
plasma experiments by flowing in gasses while pumping.  We need precise 
pressure and flow rates, and we use quality regulators (Mathesson), 
precision needle valves, etc.  But most importantly, we use closed loop 
control (via pressure or flow controllers).  Open loop control simply does 
not work.

Having attempted to make an open loop yeast bottle system work on my 20 
gallon tank,  and watching the pH wander all over the place and stress my 
fish, I concluded that was was a waste of my time.  I bought a Pinpoint pH 
controller, and a needle valve and regulator from the local welding supply 
store (I have no idea what brands) and an Aqualine Bushchke valve.  It has 
been running with NO PROBLEMS AT ALL for 18 months.

Of course, when the CO2 bottle gets very near empty, NO regulator can 
maintain pressure.  You need more gas.

If you are having trouble with an open loop system and think more precise 
regulation is required I would suggest you really need a pH 
controller.   Then I would claim that probably ANY regulator will do the 
job.  If you are trying to save money, I would also suggest that your time 
would be better spent working a part-time job to afford the right 
equipment, rather than fighting with a system that is doomed from the get go.


Mark Gilmore, Ph.D.
UCLA Electrical Engineering Dept.