[bharada]

As Sean suggested, adjusting the camera's white balance setting is the best way to get your colors to look more natural. If your camera doesn't have a good white balance adjuster you can do it post op in Photoshop or the like.

What you can do is take a reference picture of the tank with a known white and black object stuck into it. Anything non-toxic and waterproof will do. I've used white plastic knives (the disposable kind for picnics), and a black tray from a CD jewelcase. It's important that these objects be well lit by the tank's lights.

Once you have this reference picture you'd set the white and black levels based on the white and black objects. In Photoshop this would involve the Levels function. I don't have Paintshop Pro so I don't know how it's done there. Write down the values for these points and apply them to photos taken without the objects. This should get you in the ballpark.

 

[bharada]

The thing about adjusting WB post op is that you run a large risk of
blowing out some portion of the histogram when making the adjustments.
Digital photos fully follow the GIGO principle so in camera WB
adjustments are always best. That's why I always laugh at police/spy
shows that can convert a fuzzy VHS video frame into a razor sharp image.

I don't know the exact procedure for setting the manual WB on your
camera, but on my Canon S400, you put the camera into manual mode,
then choose the WB function from the menu. You then zoom in on a white
object so that it fills the entire frame and hit the Set button.

What I said about the object being fully lit by your tank light is very
important as you need to have the full effect of your lighting spectrum on
that white surface in order for the WB to be set properly.