Adrian Tappin has an introduction to feeding rainbowfishes that applies to all freshwater fish: http://members.optushome.com.au/chelmon/
deally, rainbowfishes should be fed small amounts 4 or 5 times per day. However, this is not always possible. Rainbowfishes in the wild, particularly the Australian species, usually exist under feast or famine conditions which relates to the prevailing season. The environment of the wet/dry tropics in Australia are markedly different from that of the humid tropics one finds in New Guinea. In the wet season there is usually an abundance of food. Whereas, during the dry season, when the water volume of their habitat is greatly reduced, the only food they get is whatever happens to fall into the water. Such conditions, I believe, require that rainbowfishes accumulate excess lipids in their body tissue. In captivity, rainbowfishes are inclined to overeat and if you continually overfeed them then this may lead to lipodosis (fatty degeneration of the internal organs) and eventually death. Growing rainbowfishes require a feeding ratio of 5% of their body weight in 3 or more feeds daily. However, knowing the weight of your fish is not really practical, so feed sparingly, supply enough to give 2 or 3 minutes of continuous feeding per day. It would probably be a good idea to miss 1 or 2 days occasionally as well.