Never tried the coffee filter. Have used a piece of white plastic inside of the tank, photographed that, then set that to the custom White Balance.
Whne I had the Nikon D1X it was easier because I could just put in the color temperature of the bulbs.
Shooting Raw files are also easier because you can adjust the WB on the computer after you shoot it.
Setting your parameters to Parameters2 will make the pictures look more true to life instead of saturated and contrasty, but some people like the look of parameters 1
BTW the tank looks great.