How to manage hydroponic nutrient

Proper dosing procedures and ongoing maintenance are necessary to obtain maximum performance from nutrient solutions.

1. Water quality

Reverse osmosis (RO) or rainwater are ideal because they contain no harmful salts and will not impact pH or EC. Any water stored for more than 2-3 days should be dosed with Pythoff PLUS every 1-2 weeks (0.5ml/L) then stored in the dark for at least 24 hours prior to use.

Click here for detailed information on dealing with poor quality water.

2. Add nutrient and additives

Follow the FloraMax dose chart: This will achieve the recommended EC, and optimum yield and quality.

Always add the majority of water before adding nutrients and additives. Never mix any nutrients or additives together in their concentrated form. Once a nutrient or additive is added to the water, stir well before adding the next. Silica should be added last, pre-diluted into a cup of water before being added, quickly stirred and the pH checked (Fig 13.1a).
Use the FloraMax ‘hard water’ chart for hard water (over 0.5mS) or DWC systems.

3. Check pH is 5.0 to 6.3

Check this once the total solution is made and ‘before’ feeding to the plants. Maintain pH between 5.0 and 6.3. Within this range all essential nutrient elements will remain soluble and available for root uptake.

How to measure pH: Use an electronic meter or liquid test kit. Ensure the nutrient is well stirred before measuring pH.
Target pH: If the pH tends to rise, reduce it to 5.0-5.5. This provides a larger pH safety margin than, for example, 6.0, and minimizes the amount of pH maintenance required.
Hard and alkaline waters: Avoid using recirculating systems. Also, nutrient will be more stable if pH is quickly lowered to 5.0 – 5.5 (Fig 9.1).
Adjusting pH: Add a small amount of pH Down / pH Up. Then stir well and recheck pH. Predilute pH adjusters with water prior to adding. For raising pH, it can be easier and safer to use FloraMax SILICA in 0.1ml/L increments.
Recirculating systems: Check pH daily, or after the addition of top-up water. To help minimize pH fluctuation, supply at least 10 litres of nutrient for each large plant.
pH electrodes: Calibrate regularly using *both* pH Buffer 4.0 and 7.0. Rinse the electrode with distilled water after use. When not being used, soak the electrode’s tip in an electrode storage solution – never use pH buffers or distilled water.

4. Nutrient concentration (EC)

This can be checked using an EC (or TDS/ppm) meter. However, NEVER rely on EC unless the meter is regularly calibrated.

The recommended EC: Refer to the FloraMax Dose Chart. Avoid being below this EC level. Although foliage burn may occur if EC is too high, low EC’s are typically more costly as they can cause deficiencies and reduced yield!
- The water‘s EC must be added to the chart’s EC e.g. if the water is 0.7mS, and the chart EC is 1.9mS, then the target EC is 2.6mS (1.9mS + 0.7mS = 2.6mS).
- For “ppm” meters, EC must be converted to ppm (see Table 10.2). For example, on a Hanna-500ppm meter, 2.1mS is equivalent to 1,050ppm.

How to check and adjust EC: Once the nutrient and additives are added to the reservoir, stir thoroughly then immerse the electrode. Allow the meter to stabilize before recording the reading. If the EC is below target, add extra Veg-1 until the target is reached (Table 10.4). If the EC is too high, add some water then recheck.
EC for recirculating systems: Monitor the water level and EC. Either, top up with water and maintain EC with Veg-1 (Table 10.4). Or, control the water level so the EC remains relatively constant. The nutrient should generally be replaced every 7-14 days. NOTE, hard top-up water will artificially raise the EC and must be replaced more regularly.
Over 800ppm CO2 or 1,400 PPFD: Plants will consume nutrients faster under these conditions. Raise Veg-1 by 0.5mS (2ml/L).
Nutrient deficiencies: To remedy, feed more regularly, or raise EC in 0.3mS increments using 1ml/L Ca-Mg-Fe or Veg-1.
Foliage burn: Salt build-up in the root zone is the most common cause. Remedy by flushing more regularly and feed until 10-20% run-off.

5. Feeding

The feeding strategy is critical for achieving optimum root zone nutrient levels. This ultimately depends on plant/pot size, substrate, PPFD and VPD. Refer to Table 10.3 for ‘Feeds per day’ and ‘Run-off %’. Always feed frequently and ensure the entire root zone is fed and flushed via 10-15% run-off. Run-off helps to keep the root zone cleaner with less salt build-up.

Top-feeding: Assign multiple drippers per plant, and arrange so there are no dry spots. Devices such as water-rings or spray nozzles are a good alternative to single point drippers (Fig 2.1).
Check run-off periodically: For run-to-waste coco coir or soil systems, periodically collect some of the run-off and check its EC. If it measures more than 0.5mS (500 µS or cF 5.0) above the EC of the input nutrient solution then consider flushing through with a milder solution (or even pure water) to help clear the root zone of excess salts. For example, if the nutrient solution has EC 1.7mS but your run-off measures 2.3mS (or more) then it is time to flush.

6. Nutrient stability

To ensure the nutrient operates properly, adhere the following points:

Conditioning the nutrient solution: Poor growth is often from failure to condition the nutrient solution. FloraMax Pythoff PLUS and System Maintenance are ideal for this (Fig 11.3). Unlike, chlorines and peroxide, they are both fully compatible with FloraMax additives, and are gentle on roots and have a much longer half-life.
Cover the nutrient reservoir to prevent evaporation and light exposure: Light can destroy organic additives and chelated trace elements, and accelerates the growth of slimes and pathogens. Also, cover other regions of the system where nutrient is exposed to direct light. For example, the stem base and the top of open trays and channels. When placing a lid on the reservoir, have it in a raised position so that air can freely enter and exit (Fig 13.4).
Avoid using an nutrient aerator in run-to-waste systems. From a plant growth perspective, additional aeration (e.g. via air-stones) is generally unnecessary because the nutrient is not being recirculated. Importantly, aeration can destabilize nutrients, and causes blockages by accelerating the build-up of white calcium scale.
Nutrient aeration in recirculating systems: Oxygen in the nutrient is consumed by the roots and will deplete with time. Therefore, aeration is required to rejuvenate the oxygen levels. Maximum aeration is achieved by breaking the water up into small droplets via tumbling or spraying, or via an air-stone and pump. In either case though, ventilate the space where the aeration occurs otherwise it will become depleted of oxygen.
Monitor the temperature of the nutrient solution. The ideal is 20 deg C (68 deg F). Warm nutrient risks promoting root diseases or suffocating the root zone with low dissolved oxygen levels. Cold nutrient will shock the roots and slows plant metabolism to a crawl. If heating of the nutrient solution is required, submersible water heaters are commonly used (Fig 13.5). Where cooling is needed, water-chillers are effective. Positioning the nutrient reservoir in a significantly different temperature zone outside of the growing environment may help alleviate the need, or cost, of providing additional heating/cooling in some situations. In extreme climates, extra insulation can be gained by burying reservoirs underground.

7. Root zone flush

Flushing removes salt build-up and dirt from the root zone, substrate and feed circuit. Generally flush every 1-2 weeks, or weekly if water quality is poor.

Step 1. Once the nutrient reservoir is empty, remove any obvious build-up then partly refill with water.

Step 2. Add 0.5ml/L Pythoff PLUS and ensure pH 5 – 6. Operate the pump for 15-30 min to flush the root zone, substrate and feed circuit. For coco, soil or Rockwool systems, pump until the run-off is within 0.5mS of the input water.

Step 3. Repeat the process if the waste is very dirty.

Step 4. Inspect filters and drippers prior to making fresh nutrient as these can become blocked during flushing.

8. Post harvest clean-up

This helps prevent diseases in the next crop:

Step 1. Remove plants and non-recyclable substrate then do as much manual cleaning as possible.

Step 2. Partly fill the reservoir with water. Ensure pH 5 – 6. Add Pythoff PLUS at 2-4ml/L and mix well. Ensure good ventilation and low light.

Step 3. Run the pump at least once every hour over a 24-hour period. ‘Flooding’ may be necessary to contact hidden surfaces.

Step 4. Discard this solution then flush several times with fresh water to remove excess Pythoff PLUS. Drippers may need to be dismantled and cleaned.

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