Play with the white balance settings. Either try to find one of the presets that works better than AUTO, or if your camera lets you, input a custom setting. As high as you can go. 6000k would be if you were shooting outside in the sun, but that is why your tank looks so blue. You need to choose something like a 10,000k or even higher. Basically whatever your bulbs are, your camera should match this. The problem is that most cameras won't let you have a white balance setting that high. So get it as high as you can and then use software like lightroom or photoshop for final tweaks.