How can I properly maintain my hydroponic nutrient solution? 

Reservoir maintenance is the routine task of keeping the hydroponic nutrient solution in the reservoir from becoming too strong or toxic as the water is being evaporated and the nutrients within the solution are taken up by the plants. Simply put... Top off daily with half strength nutrients, alternating days topping up with plain water. Change the entire reservoir with fresh solution every ten days to two weeks. Why should you? One problem in hydroponics solution maintenance, is that as water is evaporated out of the solution, the concentration of nutrient salts in the solution becomes gradually stronger to the point of being toxic to the plants. The total disolved salts will become stronger as water evaporates. Another problem, is that hydroponically grown plants will take up what they need as they need it from the nute solution. A nutrient solution left alone will end up lacking key nutrients, with a build-up of *toxic levels of other key nutrients. *Toxic in the solution, as well as in the plants. The only way around these problems for the average hydroponic grower, is to practice sound reservoir topping off procedures. The most widely accepted maintenance method, involves daily topping off and routine reservoir solution replacement. Topping off the reservoir daily with a nutrient solution which is half of the current new reservoir strength, alternating days by topping off with plain water. Changing the reservoir solution every two weeks, will give the plants a fresh and well balanced nute mix, which has not been altered by the plants nutrient uptake. * **Many scientific studies have been performed, which prove these facts by GCMS testing of the nutrient solution contents and the nutrient salts contained within the plant tissues, as the plants "take-up" the specific nutrients in the solution. Metaphorically speaking... Plants will take up excessive levels of some nutrients, leaving the solution lacking in certain key nutrients. Just like a puppy would make him/her self sick if it were allowed to feed from a bottomless food bowl. Plants grown hydroponically can harm themselves with nutrient deficiencies, lockouts and overdoses, if allowed to continue feeding without some control over the "food bowl".