If you want to test for nitrogen, phosphorous and potassium you will have to spend a lot of money for a test kit, then buy some standard solutions to use to calibrate the 3 tests. That can be a fun thing for a few months, but eventually it will be a job that you will begin to find excuses not to do. That's why the estimative index method is so good - easy to follow, little work, no test kits. You need to be able to make big water changes easily for any tank, no matter how you fertilize it. If the water supply is in the basement, and if there is a drain there, it is very simple to install PVC piping up to the tank, through the floor, so water changes involve nothing but opening and closing valves. When you add more than 10% roughly of the tanks volume with tap water you need to also add a dechlorinator, with Seachem Prime being a very good and economical one. Many, many people do this without problems.