Heres my two cents. Before you fertilize, you have to make sure your water alkalinity is higher than 20 ppm.
How much to fertilize depends a lot on your water clarity. Ideal water clarity is between 18 to 24". The clearer the water , the more fertilizer to apply. For example if water clarity is 30" you may want to use one gallon of liquid fertilizer per acre.If clarity is 5 feet you may want to use 4 gallons per acre. If you are using granular of powdered fertilizer then you go by the pound.
Check out the fertilizing section of this website, at top right of that page select the option for "show all topics" then browse through em all. That will help a lot with stuff like liming, converting liquid measurements to granular, when not to fertilize, etc. Good luck!
