Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

innovative reservoir was made by lining a large galvanized pipe with heavy-duty plastic.

A float valve will turn water on to fill the reservoir when the level drops.

A two-part nutrient solution is mixed before application. Each reservoir holds one part of the solution.

Cover reservoirs to avoid extra evaporation, and to prevent contamination and algae growth.

Nutrient solution is aerated by falling through the air when it returns to the reservoir.

Attach a recirculating pipe with an on/off valve to the pump outlet pipe. This is a convenient and easy-to-control method of aerating the nutrient solution.
    To save energy and money, heat the nutrient solution instead of the air in a room. Heat the nutrient solution with a submersible aquarium heater or grounded propagation heating cables. The heaters might take a day or longer to raise the temperature of a large volume of solution. Do not leave heaters in an empty reservoir. They will soon overheat and burn out. Aquarium heaters seldom have ground wires, a seemingly obvious oversight. But I have yet to learn of an electrocution by aquarium heater. Avoid submersible heaters that give off harmful residues.
    When air is cooler than water, moisture rapidly evaporates into the air; the greater the temperature differential, the higher the relative humidity. Maintaining the nutrient solution temperature around 60°F (15°C) will help control transpiration and humidity. It will also promote the uptake of nutrients.
    An air pump submerged in the reservoir not only aerates the solution, it will help level out the temperature differential between ambient air and reservoir.
Irrigation
    Irrigation is a science unto itself. Irrigation cycles depend on plant size, climate conditions, and the type of medium used. Large, round, smooth particles of substrate drain rapidly and need to be irrigated more often–four to twelve times daily for five- to thirty-minute cycles. Fibrous mediums with irregular surfaces, such as vermiculite, drain slowly and require less frequent watering, often just once per day. The water comes to within one-half inch (1.5 cm) of the top of the gravel and should completely drain out of the medium after each watering. Top-feed systems cycle for about five minutes or longer and should be irrigated at least three times daily. Often growers cycle the nutrient solution 24 hours a day, especially when growing in fast-draining expanded clay or similar mediums.

Large non-submersible pumps quickly and efficiently move considerable volumes of nutrient solution.

A removable foam filter on the intake of this submersible pump removes particles that could clog the impeller and feeder tubes.

A handle and stand on this pump make it easy to move and mount into a fixed position.
    In fast-draining mediums, overhead irrigation is continual. Drip irrigation in coco coir is four or five times daily. Flood and drain irrigation cycles are five to ten times daily.

Reservoir temperature range

Use an aquarium heater to warm cold reservoirs. Do not let the reservoir dry out when the heater is on or it will burn out
    During and soon after irrigation, the nutrient content of the bed and the reservoir are the same concentration. As time passes between irrigations, the EC and the pH gradually change. If enough time passes between irrigations, the nutrient concentration might change so much that the plant is not able to draw it in.
    There are many variations on how often to water. Experimentation will tell you more than anything else.
Nutrient Disorders
    When the hydroponic garden is on a regular maintenance schedule, and the grower knows the crop well, nutrient problems are usually averted. If nutrient deficiency or excess affects more than a few plants, check the irrigation fittings to ensure nutrient-challenged plants are receiving a full dose of nutrient solution. Next, check the substrate around affected plants to ensure nutrient solution is penetrating entire medium and all roots are wet. Check the root zone to ensure roots have not plugged drainage conduits and are not standing in stagnant solution.
    Change the nutrient solution if there is a good flow of nutrient solution through the root zone, but plants still appear sickly. Make sure the pH of the water is within the acceptable 5.5-6.5 range before adding new nutrients.
    If changing solution does not solve the problem, changing to a new brand of fertilizer may do the trick. Check out the color drawings of specific nutrient