New Grower PPM TDS EC and so forth

[mrmojo420]

I am new to hydroponics. I have an ebb and flow system with a 55 gal resevoir. I dont want to have to replace all the nutients every time I feed, it would cost me a fortune in food. I have read about people topping off their tanks with nutrient solutions. My problem is that while I understand about PPM TDS and EC Im not sure how to translate the numbers into my feeding schedule. Im using foxfarm nutes. Their feeding schedule give EC and PPM levels but Im not sure how to mix the food to achieve them. Do I take into account the PPM level of my water (my tap water has about 300PPM) before adding nutes and add that to the level that foxfarm indicates or do I just bring the level up to what foxfarm states? Can I just mix a five gallon bucket of nutes per the scedule and add it to the resevoir when its down or do I need to do something else? I have a lot of questions and I dont want to get started before I feel comfortable with the process. If someone knows of a tutorial that I could check out could a drop me a link to it? It would be very much appreciated. Thanks in advance for all the help both past and present.