Clive,
Yes they were. I turned off the co2 and made a bit water change. No one dies. And they get back to normal.
Even after 6 hours the co2 went off, the filter sometimes pumped bubbles from the outflow and make little noise (like dripping tap). I had to open it and introduce water from the aquarium to filled it at the top, close ti, and then suck with my mouse from the outflow to "bleed" him. After this it´s ok. This morning no noise come from the filter and no bubbles from the outflow. All normal in the tank.
So i put the Diffuser back to it´s position.
I guest i find the answer i was looking in a description of yourselve from 2010:
"For now, the best we can do is to turn the gas on much earlier than we need to, say 2 hours before lights on. In this way the peak equilibrium concentration can be reached just at lights on, after which time evaporation + plant uptake will keep the levels from rising. Then you can turn the solenoid off a few hours before lights off. It's not necessary to run the gas until exactly lights off. The critical time for CO2 is at lights on and the first few hours thereafter. This is when tanks are made or broken. It's OK if the concentration starts to fall in the second half of the photoperiod. In this way, if you turn the gas off much earlier, you lower the concentration during the dark and early morning periods and thereby reduce the stress on the fauna."
Acording to this I think that 4 hours should be more than enough with the amount of the injection i have. Yesterday, the co2 starts two hours earlier than the lights and i get the maximum input as the lights went on (PH drop from 7.6 to 6.8 / 6.6).
Than as i mentioned before, because of the fish i had to shut of Co2 two hours after the lights went on.. but you know? The drop cheker was still yellow at the end of the photoperiod.! 4 hours after.
So i assume i can work with a 4 hour injection or i can reduce just a bit and have the Co2 working for 6 hours instead 8.
Bottomline: The Co2 doens´t have to be pumping gaz as much time as the lights are on.
This is what i conclude.