I would think that it has to be a white balance problem.....what method are you using to set the white balance?
What I do is switch to manual mode, set the ISO that I'm going to shoot with, as well as my expected shutter speed and F-stop. Then I zoom in on the whitest substrate I can find...focus as well as I can, and use the manual white balance to set it.
If there is not substrate that is really white, another option I have used is to drop a white lid from a container of carbon or something into the tank and point my camera at that to set the white balance.