Water change timing

[Wet Elbows]

I've always wondered about this. In a CO² enriched aquarium, when is the best time to do a water change?
Part of my brain thinks that since you're lowering the water level and exposing plants to atmospheric CO² any time is a good time.
The other part of my brain thinks about reaching saturation point with the associated pH drop then changing water and raising the pH, and then having the CO² lowering the pH again before shut off, and that's too much pH swing for fish to handle in such s short time.
So what's the correct answer?

 

[Naturescapes_Rocco]

Like so many things in the hobby, there is no way for there to be one correct answer! There are just pros and cons to consider.

I ALWAYS try to perform my weekly water changes and trimming/maintenance either towards the end of the photo period, or just as the lights are turning off.

Letting the tank have 7/7 days of full photoperiod each week, without major disturbances, matters for me -- especially since I favor large (70%+) water changes.

If I were to perform these large WC during the day, I'd end up reducing my CO2 injection to ~30% of where I want it to actually be during the photo period for 1/6 days every week. Not ideal, in my opinion! So yeah, I always do water changes in the evening or towards the end of the photo period, as to give the tank the most undisturbed and useable time through the week.

 

[klibs]

Depends on the setup. IMO don't overthink it. I usually do mine at the end of the photoperiod or at night to avoid light cycle with minimal CO2.

If your setup will be fine getting light with less CO2 then it shouldn't be a big deal at any time.

 

[JayP]

I like to stick to a routine. A couple of my tanks get water changes at the end of the photo period every Friday and a couple tanks get their WC every Saturday early morning before CO2 kicks on. Once I set up more tanks they will be on similar schedules but probably on other days. Things will be so much easier once I retire.

 

[Kwyet]

I do my water changes/maintenance in the morning, when it’s convenient for me. I don’t worry about how it works with the CO2 or lights anymore. I used to think it was important to do before the CO2 came on, but I’ve done it now at various times of day and not found that it made any significant difference.

 

[Pepere]

I fit my water changes whenever I can on either a Saturday or a Sunday…

I figure better they get done every week than timing them perfectly…

Today I had to move 4 inches of snow this morning at a few different properties…. The water changes got done this afternoon on the upstairs tank.. basement tank will be when I can fit it in tomorrow…