Well that lighting seems pretty reasonable to me mate. JamesM had mentioned to me that he saw an improvement in one or two of his tanks when he altered his water change schedule. This led him to the conclusion that the time of day was a contributing factor. The problem is that he had also made several other changes over the period of a few weeks along with an adjustment to the change schedule. So it's difficult to draw any conclusions about a particular variable when other variables are not held constant. Additionally, some responses to environmental changes are either not linear (i.e the change in output is not proportional to the change in input) or occur over time - for example you can do something today and not see the results that are directly related to what you did for a week or more.
So really, although I'm not doubting James' observations, I guess I'm not convinced that the time of day for WC should play a significant role.
I'm going with James on this one
I think it does make some difference.
Try it like this, do one right after the lights go off.
Then try it say 1 hours after the lights go on
See what occurs that night before lights go off(there's a few hours difference due to the timing, but this cannot be helped). I think you'll note much better pearling and O2 levels=> better growth, if you do the large water change right after the lights come on, vs the night before(12-4 hours prior to the lights "on").
Try it and see.
Look, you cannot over do water changes on planted tanks, they can only help right?
Nothing to lose other than some water, cheap ferts, time etc, then you can clean and take care of other nagging chores for the tank/s.
So try it out. I do a 80% water change the day of an open house about 30-60 minute after lights come on, then the folks show up about 4 hours later, hang out, marvel are the mad pearling, I show an LDO O2 Hach meter, they all go "Ooooo, ahhhhh".
Plants take up lots of CO2 direct from the air, and the inter cellular air spaces, or aerenchyma, get filled up, and lots of O2 is also added, as well and a good cleaning of the surfaces and boundary layers, bacteria are all jacked full of O2, so they respire and give off CO2, CO2 system is also cleaned etc, filters, flow, etc better.
Quite a few things going on.
But purely observational test, try it 1 hour after, then try it 1 till the lights go off.
See what you think. You can also try this: crank the light doing what I do for that day, vs trying to do it if you do the WC at night.
Watch and observe close.
This is one reason I started doing larger water changes, they allowed me to grow the plants better than other folks.
I also believed the water quality was higher and better for fish when I did 50% or more weekly.
Try it and see.
Some tap is also loaded with CO2, some less so.