Try something like this....
Premier Line - SuMo CO2 Regulators for Planted and Reef Aquariums
I got the one with the bubble counter and actually took it apart to put the knob on the needle valve downward. Someone ( I think on this site ) had them build him one with dual solenoids and needle valves to control two different tanks. The single regulator worked just find for him.
The only minor issue I found with them. They're heavy. When they say to secure the tank, DO IT. I was lazy and was tweaking something and put the tank on the carpet and the whole thing fell over. No way does this reflect on them, it's just good practice to secure the tank. The really good needle valves cost money, you don't want to replace them because you were too lazy to secure the tank.
Pay the money up front and be done with it. The cost of a quality tool is soon forgotten. You will always be reminded of the cost of a cheap tool every time you use it. Unless you REALLY like LCD displays I'd suggest just going with a more conventional CO2 regulator combo.
Rex Grigg's model is similar and the cost comes out ~ the same once you put in the same upgrades. Again, if you want all the blinky lights and such, these probably aren't for you.
The Best Aquarium Regulator & CO2 Parts
Given how CO2 delivery and flow in the tank affects the distribution so much, I don't think having the ability to deliver CO2 with picoliter precision will get you much. There is a point of diminishing returns and your probably far better off giving something a trim in the tank that's blocking the flow than dialing in another .038 grams of CO2.
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