When choosing an appropriate site for a hydroponic setup we sometimes overlook the quality of the water which supplies the site. The way you water your plants and the amount of water you give them can be a major factor in the overall health of the plant. You have to ask the question "how clean is the water?". Most town water should be suitable for plant growth, however having said that, I would advise you to invest in a water purification system, not only for the plant's benefit but also your own! It is my view that you just don't know what your water suppliers are throwing in the water supply to make it safe to drink.
A few years ago we experienced a Cryptosporidium and Gardia outbreak in Sydney. As well as people getting sick, we had a major problem with a rush of growers coming to us with rootzone problems. No matter what they did the problem continued to haunt them. Initially, they blamed everything from the nutrient they were using to propagation gels, additives and us personally. As we investigated each case we found that even though all systems, lighting, airflow, growing methods and nutrients used were very diverse, all growers had the same problem. Naturally we looked for a common denominator - which of course was water. Some clients were hard to convince, considering they were on 'town supply' and therefore the over-riding belief was that the water quality must be of a high standard, i.e. if it's safe to drink it must be OK for my plants. Not so.
Did you know that over 50 different chemicals can be legally added to our town water supply in order to make it safer to drink without us even knowing? Listed below are just a few of the major ones which can also effect your plants:
Calcium Oxide or hydroxide, potassium aluminium sulphate, liquified chlorine, sodium silicofluoride slurry, sodium hypochlorite solution, fluorosilicic acid, and various other electrolytes. This is not taking into account the number of chemicals that are added to our water supplies unintentionally. Most of our catchment areas are exposed to the elements, some of which may include lead, copper, pesticides, herbicides, asbestos and raw sewerage to name a few. I've seen plants that look absolutely amazing when small and as soon as they are exposed to the main system, they crash. Why? Water quality. Even if you are drawing your water from bores or rain water off the roof, you still run the risk of not only collecting water, but a high mineral load which when fed to your plants can affect the nutrient levels, potentially giving your crop toxic shock.
Rusty, galvanised or copper pipes also contribute to higher levels of heavy metals such as zinc (zincalume) and iron in the solution. If these metals are present in any quantity, your plant will experience toxicity symptoms even if you are using a balanced full spectrum nutrient. A good way to check if your water is suitable is via a digital salt meter (nutrient tester) . If you get a reading in water above 1 CF you would be wise to consider a water purifier of some sort. The purer the water and the more neutral the pH in your water supply, the better. Before I continue, I have to tell you that out of all the clients who were experiencing rootzone problems, only one continued having problems (eventually driving the client to abandon hydroponics) because he was the only one who didn't buy a water purifier. For a small investment of around $200, he lost a fortune, (think about that!)
Over watering is a common problem with novice and experienced growers alike. (Commonly known as 'killing plants with kindness'). Most growers assume that the plant will take as much water as you can throw at it. This is another fallacy. If the water you are supplying to the plant does not have the right oxygen, nutrient, pH and water mix, the plants can actually drown in a saturated mess. Oxygen is unable to get to the plant and consequently they start to suffer, developing symptoms of a deficiency. Brown blotchy leaves turning down and starting to wilt. The grower panics and throws more water and nutrient in the system, unwittingly overdosing their beloved plants, end result... the plant dies. If you experience this, you need to drain off the media completely. You can gradually bring the plant back to good health by feeding it oxygen rich pure water. Good drainage is essential to the recovery process, therefore consider the media (substrate) you are using. If you are doing everything right, new growth should start to appear in approx. 2 weeks. Plants generally take about that long to recover from a stress situation.
Under watering has very similar symptoms, however they can occur more quickly with more dramatic consequences. It can be a scary sight to check your garden and find your entire crop has suddenly wilted overnight. It can be only one thing: no water. Check that your water pump is working and is clear of any root matter or fine media particals. This means take the pump apart and clean it thoroughly. If this is the problem, it is easy to rectify and the plants should recover with no noticeable damage within a couple of hours. Once the watering cycle resumes, hourly checks to mark the recovery progress would be advised. Regular maintenance of everything that services the growing environment is essential, which will ultimately lead to a successful end result. Try to visit your greenhouse or grow room once a day to avoid any of the above mentioned catastrophies, especially during the flowering stage. Think of it this way, "a little maintenance a day keeps the problems away" and you'll get to reap the benefits at harvest time.
Oxygen keeps a plant's root zone healthy and allows the uptake of nutrients. Oxygen is the key to a high growth rate. Without oxygen around the roots, the root cells would die leading to rootrot (pythium) problems and the eventual death of the plant.
You cannot grow in water unless you have dissolved oxygen in it, so a well oxygenated nutrient solution is essential for a healthy rootzone. The fine root hairs take up the nutrients and oxygen, and obviously the more root development, the more nutrients the plant can take up, hence a healthier plant and better yields!
If you have still and stagnant water you're asking for trouble because that will cause root death due to oxygen depletion, which in turn could cause Pythium (a fungal disease) to run rampant, or even attract harmful bugs like the scarid fly (Fungus Gnat).
Recirculating Systems add that essential element to hydroponics: OXYGEN. When oxygen increases, so does growth, and in many ways it is more important to consider than nutrients.
Rootzone temperature also plays a very important part in overall tank control, and the ability for plants to take up oxygen, water and nutrient. The ideal rootzone temperature is between 20 and 24°C. If the temperature falls below 20°C plant growth will begin to slow, and if it reaches 14°C, plant growth will stop altogether. On the other hand if the rootzone temperature rise above 24°C the need for oxygen by the plant increases as the dissolved oxygen that is in the tank decreases. This can have a devastating effect on the plant and can accelerate outbreaks of pythium spores and other rootzone diseases.
Masta golden rule of oxygen - plants cannot take up their nutrients unless oxygen is present. The more oxygen, the faster the uptake of nutrient...but watch the temperature too!
Configuring a Venturi