I can try the yellow water test, but I just don’t think that it will be noticeable either way in a small sample of water.
Here’s a photo from the far end, 200 cm tank, you can see it gets progressively yellower.
I don’t currently have any fresh water systems and no wood in there
Just swapped in new bulbs, new T5 and new halide bulbs (14K from Geisemann).
btw the the tank is always slightly hazy from sand, because I used very fine sand and then put in some sleepee gobies. That was a mistake, but there’s no way I can catch them now…