[pelicanincident]

I'm having the exact same issue. Same solenoid and needle valve, but I use a plastic check valve. I set my bubble rate before it shuts off at night. Come home from work the next day, and the bubble rate is half of what it was the day before. Frustrating as hell. Other related posts mention moisture getting to the needle valve or a low quality valve. I have had a check valve inline since the beginning, and I know the Fabco needle valve is a quality valve.

Two observations:

One, I know for a fact my co2 tank is starting to get low because my tank pressure is starting to drop slowly. These inconsistencies only started after I noticed this. Before that, I never had any problems. I was running my working pressure at 5psi.

Two, I tried what you suggested. I turned my working pressure up to 12psi, and this seemed to have fixed the issue for now.

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[goneRogue]

Interesting that you have a different check valve, but are having the same issue. The bubble rate has been consistent since raising the pressure. Hopefully that continues. If not my next step is to move the co2 cylinder above the height of the diffuser and pull the check valve completely to see if that solves the problem.

 

[Bettatail]

make sure there is no leak, all I can see here is typical behavior of unstable internal pressure that cause by leak.
and don't use silicone air hose if you do use it on the system.

 

[goneRogue]

I tested the system, using your steps, when I initially put everything together. No leaks. During the build I noticed that under very low flow (needle valve barely open) I could hear the check valve ball fluttering. I never liked that, but didn't think too much of it. This was also with no back pressure from the diffuser.

If raising the pressure doesn't solve my problem I'll do a full leak test again.