Sounds to me like they were just sleeping....

Matt C. wrote:
HI all- Newbie to this group here

I have a 29 gallon freshwater tank and i just spent about 2 1/2 weeks
planting the tank. I installed a 1 liter DIY CO2 system yesterday and I
noticed last night at about 11pm, that it was bubbling nicely through a
microfine airstone located at the bottom of the tank. By this time (11pm)
the tank light had been out for about 2 hours, and I popped it on for a few
minutes to check on the fish and they were all very palecolorless and
hanging out on the bottom near the CO2 airstone.
The fish are neons, glo-lights and pristella Tetras and two dwarf
gouramis. All were very subdued. If they werent getting enough O2, wouldnt
they be gasping at the surface? I dont know if this is from the co2 or not,
but I unhooked it, cranked up a regular airstone and put them to bed.
This morning they are all happy and fine with good color and swimming around
nicely.
Anyone have a thought on what I saw last night?
Thanx!