I used to do this until a member (thanks, @Edward
) pointed out some potential drawbacks with this on-again, off-again approach and suggested leaving it on 24/7, but at lower dosing levels. So, after doing some research, and finding support for this approach, I moved to it about 8 months ago. I have not noticed a change in my plants, but the dosage is lower based upon a lower frequency of refilling the CO2 tank, yet the ppm in the tank stays in the area it was before changing to 24/7. I think this is because the overnight levels are not allowed to drop and, despite my intuition saying that it should then climb at night and then be lower later in the day (after heavy consumption), my pH readings stay surprisingly consistent throughout the 24 hours.
So, why it might be good (and I can't assure you of this):
- plants and fish like things to be consistent.
- if pH is allowed to rise above 7 at night, you start to convert the NH4 to NH3 which can stress fish and eventually harm them if too high.
- the pH sweet spot for fert uptake seems to be in the 6.0-6.5 area - might as well hold it there, since it takes very little light for plants to grow (long before your lights come on).
- fish need to be adapted to our CO2 dosing (not due to the pH change) and - maybe - a 20 ppm, or more, daily swing causes daily stress, even though CO2-based pH changes don't seem to cause problems.
- algae loves disruptions and - maybe - such daily shifts add a little bit of ooomph to the complex algae development matrix.
None of these thoughts, to my knowledge, have been proven or disproved.