You would not realise it, but a simple change of the Metal Halide bulbs in your reef aquarium can make a surprising difference to both the colour and the amount of light. Here I have replaced my unknown brand 2 x 250W 14000K bulbs with 2 x 250W 13000K Giesemann bulbs. First the old bulbs:

Now with the new bulbs:

To keep results consistent I set the camera to manual settings - manual exposure and manual white balance. This allows you to clearly see the difference in intensity and colour. The second photo looks a bit more yellow than in reality because the camera was set to 10000K.

Now I just hope my coral do not suffer from light shock. Will reduce my photo period for a while.