When you get started in the world of underwater photography and you are using ambient light, a red filter is a budget friendly and easy way to begin. It can be helpful in getting better colours in your pictures.
However, a filter will also reduce the amount of light that comes into the camera, resulting in darker or hard to focus, images. Red filters remove the blue tint, but will only work up to about 15m depth. If your camera doesn’t have a custom white balance or underwater white balance option, this filter will help to enhance the colours. Otherwise, stick with manual white balance.