Methylene Blue at www.japanese-home-gardens.com

The salt solution is good for goldfish and for some, but not all, native fish. Another good fungicide, not as readily available as salt but usually obtainable at a drug store, is the dye methylene blue. This may be used with either fresh or salt water fish. It is completely nontoxic to fish, so the concentration does not have to be regulated very carefully. A common rule of thumb is to add enough of the dye to color the water a rich blue. Fish may be kept in such a solution a week or longer without harm.

BLUES Prussian blue—A strong tinting blue, very dark with a greenish cast. Good for producing brilliant greens when combined with yellow. Cobalt blue—A strong blue with a reddish cast. Good for mixing. Cerulean blue—A strong blue with a greenish cast. Ultramarine—Sometimes called French blue. It has a reddish cast and makes a beautiful purple when mixed with alizarin crimson.

Because Clerk Maxwell added red, green, and blue light together, this technique is called additive. An equal addition of the three colors forms white; red and green add to form yellow; red and blue, magenta; green and blue, the blue-green known by photographers as cyan. It is important to bear in mind that this theory holds true only for colored light; the mixture of pigments is another matter.