I see you gave this some effort. I do like the Eheim regulator, I would
not buy the pH controller from Eheim. I have used a Azoo controller and
that is a long story too.
Actually I use two of them. One is on a calcium reactor for a reef
tank. I have very steady co2 bubbling. I have used a M3 dual stage with
a solenoid and Dwyer needle valve. It did work but was a pain to get
The real problem is that high pressure / low volume systems are hard to
regulate with precision altogether, even with lab grade equipment. To
overcome this problem I used a brass check valve with 20+ psi cracking
pressure is used. So what gets through the check valve is controlled by
the needle valve assembly to the check valve. Probably only 1-3 psi
difference and still has enough force to drive diffuser on exit.
When using a dual stage to a needle valve adjustment, the back pressure
after the needle valve will be almost non-existant. So for example
running a second stage at a lower level is necessary to get a fine
adjustment out of the
needle. It can work but I am tired of trying.
Hope this is of some use to you! I really cant provide info on the
needle valve. There is currently on for sale on ebay though.... :