If he/she is doing water changes every week / every other week is this even possible? Personally, I hesitate to make any decisions based on color related questions as there is no way to know the color temp of the light or the compensation that was made by the camera/software.
It is possible to do water changes and still have nitrogen products in the water. You are right, the yellow could be from lights or his camera, but I'm assuming his T5HO are fluorescent and Cool White. To me it looks like his water because other things like the reflection of the heater and the clear tubes in the tank are not tinted yellow, but breeder box looks like it is.
I have a tank that looks exactly like this used to grow macroalgae and the water is the same color as his, the same color as the water in the neglected goldfish tank where I get the water for my algae tank, which oddly enough has the same kind of algae.
I am pretty confident it's a combination of too much light and too many nutrients.
The last time i checked my water conditions my ammonia and nitrite levels were 0 ppm and my nitrate was about 20 to 40 ppm (hard tell from the color chart).
The algae is green algae is all on the glass, although i think i have BBA on my rocks. I usually about a 40% WC each time.
I use Do Aqua Be Green for my trace elements every other day.
I have 2 T-5HO for lighting
When was the last time you checked?
You say you are diligent in maintaining water quality, but if this was the case you would not have such an insane amount of algae.
Algae uses the same nutrients plants do, so perhaps there are too many nutrients and not enough plants to compete with the algae.
Algae also blooms when there is a surge of ammonia or nitrogen products, which happens when you don't change the water for a couple of weeks.
Algae spreads because of excessive photo-periods
. You have strong lights, how long are your lights on every day?
A side note: You can turn off your Co2 at night, plants only use it when photosynthesizing and switch to O2 when the photo-period ends. Save yourself some Co2.