Following pertains to plant minerals and pH levels. Dilute 1 tablespoon of fertilizer in a gallon container with water at a time before adding to system. (Adding too little is safer than adding too much). For non-hydroponic fertilizers use 1/10 of the dosing on the label, with the amount of water in the container in mind. The hoagland solution provides a basic reference point. (Please do more research on this).
Calcium, carbon, hydrogen, magnesium, nitrogen, oxygen, phosphorus, potassium, and sulfur are essential macro-elements. Oxygen, hydrogen, and carbon are obtained from water and air.
Nitrogen, phosphorus and sulfur can be fixed by certain endophyte bacteria.
Boron, chlorine, copper, iron, magnesium, molybdenum, zinc and possibly nickel are essential micro-nutrients.
Hard tap water contains many plant nutrients.
Measuring the conductivity of the water (using a multimeter) is a way of analyzing the total dissolved solids. This indicates whether the water solution is within range, but this method doesn't test for nutrient imbalances. Test paper, or a pH and nutrient meter is required for more testing.
- 1 ppm=1 mg/l 
The weight ratio of an essential element within a nutrient compound needs to be found, and the atomic weight of these elements and a chart is helpful to solve this.
Do not add mineral tablets (except calcium?) not made for fertilizer purposes to the nutrient solution. The nutrient solution should be clear when the system is set up.
- Resh, Howard (1998). Hydroponics: Questions and Answers for successful growing. Mahwah, New Jersey: New Concept Press. ISBN 0-931231-96-5. http://www.howardresh.com/Howard-Resh-Books.html#.