I've been able to find the optimum levels of n-p-k and Mg (ppm) for cattleyas, but I can't find optimum ppm of Calcium. Cattleyas are prone to calicium deficiency showing up in the tips of new growths in the form of leaf tip dieback and black rot. This happens because Ca is a non-mobile or only barely mobile. I have two cattleya seedlings (maxima) that are showing these types of symptoms and since the leaves never get wet and I never have cold, wet conditions, I am pretty sure it's a calcium deficiency. I use reverse osmosis water and an all purpose RO orchid fertilizer with a bit of calicium, but I think it's only 3 percent. I was able to find that cattleyas need 50ppm of magnesium (the same ppm they need of nitrogen), so I have been supplementing once a month with 1/4 tsp per gallon of Epsom salts when not using regular fertilizer, but it need to know what the proper amounts of calcium are before I choose a cal/mag fertilizer.