Everyone's goal is to have nitrate as minimal as possible. Some want to run a slightly dirty tank with 5-10 ppm nitrate. Others want that 0 mark. When testing and you get the holy grail of 0, but you notice those slight scruffs of HA, what is the actual levels of nitrate? There has to be some as it is getting used as fuel for the algae growth, but if test so 0, how does one know the actual amount of nitrate in the water? This is especially true if one wanted to carbon dose to help with the nitrate issue.