My plants all seem to have bounced back and adjusted to the lack of fertilizer dosing. I assume there is still lots of available nutrients in the substrate (Eco Complete capped w/ PFS and pacific gravel) due to root tabs that have been added at multiple intervals. Also, now that everything is mature and stable (it's been almost exactly a year since the big tear-down and rebuild of the 10g into it's current configuration), it seems to be dealing with the new CO2-only configuration quite happily. Plants are growing more slowing (kind of nice, really) and do look a little different, but have coloured up and filled in very nicely.
Shrimp are still surviving, though I haven't noticed any juveniles yet. I have noticed a few berried females, however, so hopefully they're in there. I'm confident I will finally get a healthy breeding colony out of this attempt. Hopefully.
I did, however, install some experimental upgrades to my DIY CO2 system that are currently in the test phases and seem to be doing well.
Basically, I installed a solenoid valve to shut off CO2 production at night. Previously I have just been running an inline air pump which shoots bubbles out of my lily pipe outflow and gives lots of surface agitation while the lights are off. This worked well, but it splashes water around and makes it annoying to keep the water level right at the top. Not a big deal, but I wanted a new project and this was my first thought.
I ended up buying a cheap solenoid on eBay for $17 shipped. Problem being that it works on 220v only, so I also picked up a 110v to 220v converter for another $4 shipped.
I installed it inline right before my first needle valve and, after some adjustments, it seems to work great!
I drew up this quick schematic in paint (as it's easier than explaining it via text):
I have 2 yeast bottle generators (tan) being fed into a gas separator (light blue), then through the solenoid valve (red), one needle valve (green), the bubble counter, a second needle valve (green) and then on into the reactor (grey). Yellow represents brass check valves and blue are manual cut off valves for bottle replacement.
I've never been worried about popping a bottle, as I frequently shut my production down manually overnight to waste less CO2, but I just hate remembering to do it manually. Still, to be safe, I had to think of a alternate way to vent excess pressure at night. The easiest, most cost-effective way that I came up with was to add a 3rd needle valve and tubing fed out of one of the generators. From experience, I know that a single cheap chinese needle valve is not enough to cut the flow off entirely (hence why I use two in series... for finer control, but also allows me to shut it down by closing both) and it will leak, but only under maximum pressure.
I knew this would allow some pressure to escape at night, but in order to know how much, I also installed a bubble counter on this output for a visual reference. At night once the pressure builds up, I end up with a steady 1-1.5 BPS coming out of this safety valve and venting to the atmosphere. During the day I only get flow through the main bubble counter, not through my safety relief, so it seems to work like a charm.