Just to clarify a note on perfect parameters including P04. If you have hair algae, then the results are not perfect and I will try and give a loose example. If your tank is producing 5ppm of P04 through feeding and waste, but the hair algae is eating 4.9ppm, then your test will show 0.1ppm. So you could be feeding it, only the algae is eating it as quickly as it is being produced. You need a media to remove P04 quicker then the algae can eat it. Which is what a remover such as GFO will do. That is one of the reasons it takes so long for results to show. You literally need to starve out the algae. As it dies off, it creates more P04 to feed the living and that needs to be removed before it is consumed.