Continuous Flow Hydroponic Systems

What is Continuous Flow?

Continuous flow hydroponics is a catch all term that covers a whole group of hydroponic systems. Basically, continuous flow refers to any system where, as the name suggests, the nutrient solution is being constantly pumped over the plants’ root systems.

Nutrient Film Technique (NFT) is an excellent example of a continuous flow system, as is a basic top feed or drip irrigation system. Ebb and Flow is a slightly different concept.

How Does Continuous Flow Work?
In a continuous flow system there is a constant flow of nutrient solution over the plants roots. One of the advantages of a continuous flow system is that the nutrient reservoir can be remote from the plant and its growing medium. This means that a large reservoir may be used to serve a multitude of plants. The larger a hydroponic reservoir is, the easier it is to keep temperature, pH and EC levels stable and therefore the easier it is avoid the problems that can arise from sudden changes in these values.

One of the disadvantages of a continuous flow system is that there is very little room for manoeuvre should something go wrong. An overnight power outage, for example, will be likely to kill all of your plants. This ‘eggs in one basket’ aspect of the system should be weighed against its superior productivity.

By making the dissolved nutrients so readily and constantly available to the plants’ root systems it is possible to achieve explosive growth and some of the most productive hydroponic systems available rely on the continuous flow concept.

This of course necessitates the grower somehow providing oxygen for the root systems and this is done in either one of, or a combination of, two ways:

• The nutrient solution can be oxygenated in the reservoir by means of an aquarium pump or other bubbler. With this method the oxygenation is occurring remotely from the actual plants roots and there is time for it to de-oxygenate slightly en route to the system. Because of this it is important to make sure that the air pump is powerful enough to really get plenty of air into the solution;
• With systems such as NFT, the roots are only partly suspended in the nutrient solution. Whilst the ends of the roots are immersed and able to take in the nutrients, the main mass of roots is exposed to the air where it can take on oxygen directly.

Buying a Continuous Flow System

Because continuous flow is a catch all term you may find it difficult to just go out and buy one. You would need to be more specific and search for an NFT system for example. This makes it difficult to give a comprehensive buying guide but things that you should consider before purchasing are:

• Noise – Find out how loudly the system operates. There will be a water pump and possible an air pump running at the same time. Be sure that these pieces of kit are not so loud that they will cause you, or your neighbours, a disturbance when they are running during the night time. Ask about the noise levels in decibels and use the chart below to get a better idea of what the answer means.;
• Size – Most systems will be sold according to how many plant sites are available. Be realistic about your needs. Work out how much weed you require and add a bit just to keep it real;
• Modularity – A lot of systems are modular, allowing you to easily add extra troughs for more plant sites. This is a good thing. If you under estimate your requirements (this is a very common mistake) it will be easier and cheaper to add a new module than to replace the whole system;

Depth of gullies and flow

An experiment with gullies between 60 and 150 mm wide we found that the 80 mm wide gullies and around about 40 mm deep with a slope of 1.5% were best.

We have found that a flow rate of around 0.2 litres per min or just under half a gallon a minute was optimum when gullies were approximately 3.1 m or 10 feet long. The slope of the channels in an NFT (continuous flow system) unit need not be severe. It has been suggested that 1:100 works but this is too shallow we find, a drop of 1 in 50 to 1 in 75 appears suitable which stops ‘pondng’. Maybe even look into slopes of 1:30 to 1:40 even.

DIY Continuous Flow System

Because Continuous Flow is such a loose term, there is a whole multitude of systems that you can construct that would work well and would fit the description. As with most things, building your own is much cheaper than buying new, and normally not as hard as you think. We love stoners’ ingenuity and enjoy seeing the myriad of ideas and systems that they come up with.

The first hydroponic system we ever built involved a section of corrugated plastic placed at a slight angle with a reservoir feeding nutrient solution through half a dozen tubes at the top, flowing into a gutter at the bottom, and being pumped straight back into the reservoir. The plants were placed in Rockwool the troughs in the corrugated plastic. A black plastic sheet kept the light from the roots. The nutrient solution ran in a thin film along the bottom of the troughs, allowing the top of the root mass to breathe.

This was a long time before we had ever heard of Continuous Flow or NFT!

Check out this simple video tutorial to show you how to make your own continuous flow NFT hydroponic system cheaply and easily.