Bob Taylor, chief chemist at Flairform (www.flairform.com), discusses how simple care and maintenance of our hydroponic systems is the key to maximizing growth and bloom. He shows us how to prevent diseases and pests, maintain the nutrient’s balance, and prevent the build-up of nuisance and harmful salts.

General hygiene

Together with disinfection of the nutrient solution, the importance of the above-mentioned aspects of hydroponic practice is usually grossly underestimated and, without due emphasis, good and consistent results will not be achieved. I guess downplaying the need for hygiene is an intuitive logic thing which is based on the rationale that because plants grow in dirt, dirt is OK!!

Absolute cleanliness of the growing area is a must to achieve maximum growth and minimum problems from pests and diseases. Thus, diseased foliage should be promptly removed from plants and, along with general debris, removed from the growing area, with surfaces kept clean from dust, dirt and spillages (Fig 11.1). Minimizing personnel traffic in the area, no smoking, and filtering the air supply to the area are other very worthwhile precautions (Fig 11.2).

Nutrient disinfection

It’s common to hear gardeners blaming their nutrient for poor growth results. However, in many cases, the true cause is the failure to regularly disinfect the nutrient solution.

Unlike soil culture, hydroponic nutrient solutions are exposed to the atmosphere and are therefore a perfect breeding ground for many types of disease (e.g. pythium, fusarium). To prevent disease ingress, the nutrient solution, medium, roots (etc.) should be regularly sterilized (Fig. 11.3).

‘Sterilizing agents’ must yield a residual chemical when dissolved in the working nutrient so that the entire system is treated each time plants are watered. Historically, chlorine dioxide, sodium hypochlorite and monochloramine are used for this purpose.  However, monochloramine has the advantage of possessing a long half-life, is gentle on roots, and is compatible with most of the ‘organic’ mediums and growth promoters used in hydroponics.

Replacing Nutrients

In recirculating hydroponic systems, the nutrient solution must be regularly replaced. That is, it should be completely drained and replaced with fresh nutrients.  This is done to maintain the nutrient’s balance and prevent the build-up of nuisance and harmful salts (e.g. sodium, chloride), pathogen, dirt, etc.

In both winter and summer, generally dump at least every 2 weeks. The dumping frequency can be less if using rain or RO (reverse osmosis) water.

Salty water: More frequent dumping (e.g. every 7 days) may be necessary when using salty make-up water because nuisance chemicals build up more rapidly to toxic / precipitation levels – especially during hot, dry weather.

Method of dumping: Poorly designed hardware can make dumping a tedious and messy task such that there is a temptation to delay or perform less frequently than necessary. So consider this at the design stage – or before you buy. Unfortunately, most system designs are not sympathetic to the hassles of dumping. Consider the advantages of the following design features:

1.  Install an in-line 2-way valve between the pump and feed outlets to divert the nutrient flow to waste (Fig 6.1a).

2.  Ideally, design a sloping floor into the tank which drains towards a sump from which the nutrient is drained (Fig 6.1b). This will help remove the last few liters containing the bulk of the sediment. Another simpler method can be to tilt the tank towards the outlet.

3.  ‘Sump’ pumps are convenient for draining tanks (Fig 6.1c). They are light, portable and easy to prime; however, they will typically only drain to a depth of around 1 inch. Hence, a sloping tank floor or built-in sump is needed for best results.

Where to dump: Utilize the remaining nutritional benefit by placing it on your garden or applying over a large area of grassland, etc.  Do NOT put down drains, toilets or in waterways or pour into sand as this can cause environmental damage (e.g. algae bloom).

Flushing of root zone with fresh water

Hydroponic systems must be regularly flushed and cleaned with fresh water. (Also, note that for disease control, external hardware cleanliness is as important as the inside of tanks / channels.) This is done to remove the build-up of too much calcium (white precipitates – causing blockages) and unwanted / harmful salts (e.g. sodium, chloride), root exudates, algae, pathogens, etc. from the root zone, medium and other system parts.

Pay particular attention to flushing of the root zone and feed circuit. Further, inspect filters, inlets, and outlets, etc. prior to replenishing the system with fresh nutrient because they are prone to becoming blocked with solid material dislodged during the flushing process.

Re-circulating systems: Flushing is done immediately following each dump cycle. Firstly, do any necessary manual cleaning, i.e. remove any obvious build-up, etc.  Partly fill the reservoir with fresh water, then operate the pump with the aim of flushing the feed circuit and root zone / medium (flushing can be enhanced by spraying with a garden hose). Discard waste using the methods advised for dumping. Repeat process until waste water is clear and conductivity is close to that of the make up water.

Run-to-waste systems: Although it is relatively common for many hobbyists to flush only every 7-14 days, some commercial growers consider it necessary to flush daily! The frequency ultimately depends on salinity, temperature, medium, plant variety, and other factors.

Flushing methods are:

a) If flushing can be scheduled to occur when the working nutrient tank is empty (i.e. between nutrient batches), then the existing system hardware can be utilized. Place low alkalinity* water in the reservoir and operate the nutrient pump until the EC of the run-off water is significantly lower than the normal operating EC or no higher than ~0.5mS above that of the water in the reservoir. Where the surface of the medium is readily accessible, it can be beneficial to do additional flushing with a garden hose.

* Lower the pH of tap water to ~5.0.  RO or rain water will not need adjusting.

b) If flushing needs to be conducted more regularly than in the scenario above, then the same procedure applies. However, it will be necessary to have a dedicated reservoir and pump for flushing (Fig 6.3). This can be connected to the existing feed circuit at a junction controlled by a 2-way valve. This valve is simply diverted to this reservoir to apply flushing whenever flushing occurs.

Post harvest clean-up

Two separate procedures are required to ensure hardware is clean prior to replanting:

Disease Prevention

At the end of each crop, it is necessary to sterilize the entire hydroponic system to help prevent disease problems in the next crop. The following guide will help remove organic build-up from pathogen, algae, slimes, and dead/decaying plant matter (Fig 11.4):

Step 1. Remove all plants and media, then do as much manual cleaning as possible. External cleanliness is as important as internal.

Step 2. Partly fill system with water. Lower the water’s pH to below 5, then, with subdued light conditions, add household chlorine bleach** (50g/L chlorine) at ~5ml per liter (4 tsp per gallon).

Step 3. Mix well, then soak system for 24-72 hours. (Note that chlorine bleach will not dissolve algae or general solid material. Only wet brushing will remove those contaminants.) Suitable treatment over that time includes:
-  For re-circulating systems, run the pump for at least 15 minutes every hour.
-  For run-to-waste systems, run the pump for a short burst once every hour.

Step 4. Afterwards, discard this solution, then flush the whole system several times with small volumes of fresh water to remove all traces of chlorine, dislodged material, etc.

Step 5. Where fine drippers, sprayers, and so on are used, it may be necessary to individually dismantle and clean each unit.

Precipitate Removal

Over the long-term, it is sometimes useful to conduct an acid** flush to help remove precipitates (white precipitates of calcium sulfate and phosphate – see Fig 11.4b) that cannot be dissolved with plain water or wet brushing.

Step 1. Firstly, treat the system as detailed for “disease prevention” above.

Step 2. To tank, add water and enough hydrochloric acid to achieve pH 2. For example: if using rain or RO water, dilute 30% (i.e. normal commercial strength) by around one thousand fold, or 1 ml per liter (3/4 tsp per gallon).

Step 3. Soak system for 24-72 hours. Suitable methods might include:
-  For re-circulating systems, run the pump for at least 15 minutes every hour.
-  For run-to-waste systems, run the pump for a short burst once every hour and collect the discharge.

Step 4. Afterwards, neutralize solution up to pH 5-6 with soda ash before discarding.

Step 5. Flush the whole system several times with fresh water to remove all traces of acid, dislodged material, etc.

Step 6. Where fine drippers, sprayers, and so on are used, it may be necessary to individually dismantle and clean each unit.

** Be sure to follow necessary safety precautions and contact no metal parts.

UGM would like to issue a huge thank you to Bob Taylor and his colleagues at Flairform (www.flairform.com) for allowing us to publish this article.