How can I make my fish tank water look blue?

actinic blue bulbs give the water a great blue glow.

You can get a blue blub, or just incorporate blue elements into the tank. If you use a blue bulb, try to use a white bulb, also, or it'll look weird.

Consider instead putting a blue background on the tank, and getting some blue gravel.

We use blue bulbs in our 120 gallon, and it looks beautiful--much brighter and clearer than with regular lights. We also use white rocks on the bottom of the tank to reflect the blue light. They're harder to clean, but it's a nice effect if you're willing to make the effort.

Blue gravel with a blue background. Also some pet stores sell this dark blue stuff for ponds. You pour it in and it makes the water so dark to kill off algae. You could add a very small amount and turn your water blue.

the more blue you put in the tank the more blue it will look.

Step 1. Blue back ground (shiny blue wrapping paper)

Step 2. Blue gravel

Step 3. Blue lights

Step 4. Keep the water extra clean, any algae will ruin the effect

Just find a blue lightbulb. They are just regular lightbulbs painted with a transparant blue paint.