The fertilizer you have would be OK for your tree. However, look on the bag and see if it also contains the trace elements (Manganese, boron, magnesium, zinc, copper and etc.) Trace elements are essential for citrus. Without trace minerals your tree will always be in trouble. Fertilize at a VERY MINIMUM once a month. If you don't want to mess with constant fertilizing every now and then, you can purchase Osmocote-PLUS which is a slow release fertilizer. Each application lasts for 5-6 months, and slowly supplies nutrients to your tree with every watering.