OK, I'm going to start with the questions early. I'm sure I'll have plenty more by Sunday as I do the rest of the reading and digest what I've read so far. I've always known about white balance, but never really put it into practice. One of the things I've always wondered about, though, is the pros/cons between using white balance filters (like this) and using white balance cards (like this). Obviously one of the pros of the latter is price. Are there situations where using one is better than the other? I guess the cards may be a bit tough to use in aquarium photography. Which brings me to my last question (for now). Are there any special considerations when photographing aquariums? I.e. do we even want to custom white balance given we're used to looking at our tanks through pretty blue light?