Fertilizers that contain the three major nutrients (nitrogen – phosphorus - Potassium) and also contain all the micro-nutrients are called complete fertilizers. Most fertilizers made for orchids are complete fertilizers and contain the micro-nutrients. One that doesn’t is Orchid Focus which I actually like because the nitrogen comes from nitrate but it doesn’t include micronutrients. One nutrient that is sometimes not included in sufficient amounts is magnesium. For that reason some growers occasionally treat their orchids with Epson salts at a couple of teaspoons per gallon of water to provide more magnesium. The latest science on fertilization of orchids has produced what people refer to as MSU (Michigan State University) fertilizer formulas. MSU type fertilizers contain less phosphorous and include more calcium and magnesium. The fertilizer that works best for you will depend on your water. Municipal and well water can contain many nutrients that your orchids can use. If in doubt, I don’t think you can go wrong with a MSU type fertilizer that includes calcium and magnesium.