Your setup needs to be described for folks to better answer this. if your doing a high light, 4wpg, packed full of fast growing plants, etc, then you might be needing to add ferts daily for example. If you have a 1 standard flourescent bulb over a 55 and trying to grow java fern and java moss and are heavily stocked with messy fish, etc, you might not need much manually added ferts. So describe your setup; lighting (inculding bulb type and watts, reflector, etc.), if your using co2, and what kind of scape your after and plants you want, etc.