not sure if you can do it on iphone or not but i can adjust the white balance on my EVO 3D from auto to things like flurescent and stuff, try to see if you can adjust it and it will update the camera real time before you take a picture just pick the best one which gets the color close to what it looks like. as far as advise, try some different foods in the tank or just get some special foods for it and keep it in low light for a bit while doing this.