Hello helpful reader, Is it beneficial to add water from a tank that has CO2 injected to another that does not? I am hoping to be able to plant my much larger tank and give it CO2 almost as a treat 1 time a week or so when I do water changes.
It isn't beneficial. You need at least somewhat constant CO2 concentration in the water, and this would be far from that. The repeated surges in CO2 concentration, followed by near zero CO2 would, at best, be of no benefit, and at worst it would encourage algae to start growing.