Hi
@gray_
It's frequently mentioned that CO2 must be stable during the photoperiod, but what exactly does "stable" mean? How stable?
Perhaps a better mindset is to consider Co2 in relation to all the other components in the system, using the best of our observational abilities across time to achieve this. Empirical evidence is all we’ve got most of the time unless you want to fork out on well calibrated equipment. In a high tech system it’s desirable that all of these in principle, light/Co2/o2/Macro nutrition/Micro nutrition etc, are adequate (or above but not to a toxic/unnecessary level) but never below. This is true of Co2 and all other (inorganic) nutrients that we put into the system regularly in high tech setups.
The moment the light comes on most of us want that Co2 to be at 30ppm (an arbitrary figure to some extent) saturation in the water in high tech systems. This gives plants adequate carbon to grow if all other components are also adequate or above the plants needs.
But plants begin their uptake of Co2 at lights on (or a little after) and the amount of Co2 saturation in the water will potentially drop/dip as they uptake Co2. Can’t prove this but would say this dip will decrease the overall efficiency of the plants in your tank for the rest of the period as experience has shown they don’t get on as well if Co2 saturation isn’t maintained above their needs throughout the photo period. The dip makes this saturation level a moving target and is an example of what we specifically mean by instability of Co2 levels in a photo period.
Zeus references Ceg4080’s statement:
“When it (plant) senses a lower CO2 concentration it must increase Rubisco production, however because this protein is so complicated and heavy, the increased production requires 2-3 weeks in order to change the density in the leaf to match the new gas concentration level. So it is much easier to reduce production than it is to increase production.”
This is undesirable.
In a high tech tank you’re driving the plants hard with high light, this needs to be married with high Co2 to match this fast growth. This takes some experience. A drop checker tells you what’s going on two hours ago, not right now. If your fish are gasping but the drop checker isn’t green yet, which are you going to trust?
One way around this scenario is to diffuse Co2 at a higher rate but to have good surface agitation. This should gas some Co2 off (a downside) but caps the level of Co2 to an extent whilst providing good gaseous exchange and specifically adequate levels of oxygen for bacteria/fish/snails/shrimp at the beginning of the photo period. Photosynthesis will make o2 readily available later in the period. Tuning Co2 in efficiently like this using just a dual stage reg and a timer is gained through good observation and experience. Watch your fish, watch your plants. They’ll give you all the info you require to keep Co2 ‘stable’.