How new are you to plant fertilizing? Many of us have tried the estimative index with good success. Here is a link to get you started:
Now if you go to the end of the thread, Stu asks how to go about EI dosing; his tap nitrates are a little on the high side.
What do you need to test for? Well your plants need PO4, nitrate, traces, CO2. Several of us test for nitrates and phosphates. And pH and kH to ensure adequate CO2. Few of us test for iron though.
So what is the EI? Read here: http://www.barrreport.com/forums/showthread.php?t=1
Basically it involves giving the plants what they want, in more than adequate quantities. Let them grow. You need CO2 about 30 ppm, adequate NO3, PO4, and traces. Do a search on this forum for "estimative" to see what others are dosing for a tank your size.
Now with regards to testing, some do not test PO4 and NO3 when using this method. I test periodically though, to make sure everything is OK. I don't try to be terribly accurate, I just want to make sure everything is in the ballpark range. My tank has been chewing up phosphate, but nitrate less so. However as I am upping my PO4 dosing the plants may start to use more nitrate. I don't want either to bottom out. I am not fanatical about testing by any means. I am extremely pleased with the tank, though, for the most part I can grow anything I want. I have minimal algae.
What ferts do you need to add, where to get them? Read here, a great place to start: www.rexgrigg.com
Do your homework (above) and let us know if you have any further questions. Welcome to the forum. It is a great and friendly place.