Too much or too little food is no good either. The PPM of your nutrient solution can range from around 800 for a crop like lettuce under low light/low heat to 1600 for tomatoes under intense light and supplemental CO2.
It is of utmost importance to maintain sufficient humidity around the roots at all times, low humidity will cause dehydration and root dieback. However, you do NOT want to leave your roots soaking in STAGNANT water as this will also cause the roots to die from lack of oxygen. Dieback is visible in the form of dry, browned, and sometimes decaying roots. Once roots are dead there is no reviving them. If the damage is serious, your crop stands a slim chance of surviving.
Measuring pH is easy utilizing inexpensive test kits. There are currently two kinds, the first consists of pretreated paper strips (litmus paper) that react to different pH levels by turning color. Simply dip a test strip into the solution and compare the resulting color change on the strip to a corresponding value on the included chart. The second method utilizes a small tube which is filled with solution to which a few drops of indicator chemical are added. The results of this test are indicated the same as the paper strip test, with a corresponding color change. I prefer the later as it is more accurate. Digital pH meters are great to have as they provide instant readings but they must be handled carefully. Since extremely acidic or alkaline solutions are not only bad for your roots but also highly corrosive, care must be taken to avoid these situations. Check pH regularly when first starting out so as to familiarize yourself with the process, your crop and the system. It is important that any water used for refills or new batches of nutrient be pH balanced to +/- 6.0 (depending on crop) before mixing with your concentrated nutrient powders or liquids.
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