Designing a hydroponic automation controller with Wattmon part 1

I have been playing with hydroponic systems since several months and have found that it requires regular checking to ensure that it does not run dry and that nutrients and pH are within acceptable limits.  I have been planning to use a Wattmon to do this but only just got started.  The idea is to first monitor the system and send email alerts when user intervention is required, and at a later stage add automation to keep everything healthy.
There are many parameters that affect a hydroponic system, but the most important ones are pH, EC and water temperature.  The pH needs to be in an optimal range (usually between 5.8 and 6.5) in order to ensure proper nutrient uptake by plant roots.  The electrical conductivity (directly proportional to TDS or total dissolved solids) indicates the strength of the solution in the water.  This will vary as plants absorb nutrients or water is added.  An EC of 1.5 to 2 uS is quite commonly used.  This translated to between 750 and 1000 ppm of dissolved solids.  Finally, water temperature affects the growth of plants.  Cool weather plants suffer when the water temperature is high.  The available oxygen decreases as water temperature increases too.
The WattmonPRO has several IO lines which will be used for this project.  Two analog inputs will be used to measure pH and TDS respectively.  The onewire port will be connected to a waterproof onewire sensor.  Two digital inputs will be connected to float sensors in the nutrient tank to monitor water levels. An auto/manual switch could be connected to enable a manual servicing.
Eventually, 4 digital outputs will be connected in the following manner: 1 will open a solenoid to fill the tank with water. Three outputs will connect to small dosing pumps for stock solution A and B, and acid to regulate the pH. The 5th output could be used to control a pump or other solenoid if required.
PH is sensed using a pH probe and an interface module that generates a 0-5v signal. This is then calibrated in the Wattmon and the pH is displayed on the dashboard.
The TDS module generates a sine wave and passes a small current through probes in the water.  The amount of current that flows directly correlates to the amount of salts.  This is amplified to a 0-3.3v output and read by the Wattmon.
These values are currently being logged, and the next step is to add some automation based on the values, in a small test tank in my office before taking it to the live setup.

SeaPonics experiment part 1

So what is seaponics and why am I interested in it?

Seaponics is a method of growing plants and vegetables on diluted sea water along with some macro nutrients to provide the nitrogen, potassium and phosphorus.  The idea is that sea water contains most of the element in the periodic table, and thus will supply the essential micronutrients the plants need for a balanced and healthy growth.  It sounds far fetched at first but if you take a second to think about it, it makes sense.  A researcher Maynard Murray already experimented with this extensively and wrote a book about sea agriculture.  So this has been around for over 50 years and the question is why has it not been adopted into mainstream agriculture, especially in coastal areas?
I don’t have an answer to that but since I live pretty close to the sea and have access to what he describes as ‘sea solids’, which are created by allowing sea water to evaporate in a landlocked area and scraping the remaining solids off, I thought it was certainly worth it to give it a try.
There are various formulas for this, but I used one I found off the net and adapted it to the various fertilizers I had on hand.  Looking at the formula closely and the types of nutrients it provided via sulphates, I actually concluded that it provides everything that standard hydroponics takes care of apart from Molybdenum.  So theoretically the plants should grow just fine on this mix without the seawater.  However, adding the seawater may make them flourish – it remains to be seen.  I have started an experiment with two melons in 75l barrels.  One contains the seaponics mix, and one contains the standard hydro mix we have been using.  Both will be grown using the Kratky method, without aeration.  Here is a picture of the setup on day 1.

Standard hydroponic formula day 1

Seaponics formula day 1

I will update this blog to update you on the progress.

I also planted a Kratky type bed of lettuce with the same mixture as shown below:

Kratky bed of lettuce day 1 (shaded part) using seaponics formula

Kratky hydroponic setup in a small greenhouse

Here is a setup we helped with the other day.  A friend built a special greenhouse to test out the Kratky method of hydroponic farming.  We brought some seedlings and nutrients to add to the water. Let's see how it goes!  It is already mid March and getting hot so it may be challenging.  He put sand around the beds which he plans to keep moist in summer, this may help keep the greenhouse cooler.

Dissolved Oxygen in a Kratky System

After running the Kratky hydroponic systems for three months, from December through March, it became clear that this would not work without through summer in the tropics.  As the temperatures started to rise above 32 degrees C, the lettuce started to wilt during the day, a sure sign that something was wrong.  The water level was still high in the beds, so that wasn’t the problem.  However, the water was not looking good – it was coated with a slime and the roots all looked rotten.
After doing some more research I decided to try adding some oxygen to the water.  First, I washed all the lettuce plant roots.  Many were rotten and just washed right off.  I then placed airstones in each bed and ran a line to a central air pump for aquariums.  Within two days the lettuce started looking better and I could see the tips of the roots were now white, although the temperature had not changed drastically.  The plants that had started to bolt remained at the same height and started forming new leaves at the top.
This taught me a very important lesson:  The dissolved oxygen level in water is extremely important, and it is highly dependent on temperature.

Here are some interesting insights:

1. The higher the temperature of the water, the more it expands leaving less place for O2 molecules.  
2. Water and air exchange O2 molecules through the water surface, and this is the reason air pumps help since they agitate the water constantly, creating a space for this exchange to take place
3. A slimy surface on your water will guarantee that very little or no O2 will enter your water

So for those of you attempting Kratky in hot climates and seeing problems, try adding oxygen and see whether that helps.

Introduction to Rooftop Hydroponics

Welcome to our blog on rooftop hydroponics!  Monica and I (akash) are based in Auroville, South India and have been playing around with various types of rooftop gardening systems over the last few years. In 2012 we built an aquaponic setup together with a friend, and spent a year gathering data and fixing problems.  Our experiments ended with a massive cyclone that destroyed the greenhouse.

My experience with aquaponics

Aquaponics is a great system when it works right.  Our initial prototypes worked pretty well but when we moved to a larger system, with 6000l of water and about 10000 liters of gravel media, things became difficult to maintain.  You can see some pictures of the setup on our blog, avaquaponics.blogspot.com.
After the system was destroyed we lost all interest in farming for a while, since the results were not what we expected and the work was much more than anticipated.  Again, I would not wish this to influence anyone’s enthusiasm and I have been following Murray Hallam and his adventures and successes – it just did not work well for me.

Rekindled interest

In late 2014 I started researching hydroponics and came across b.a kratky and his experiments.  For those of you who are not familiar with him, he is a professor at the university of Hawaii and he came up with a non-circulating system with suspended net pots that make it very easy to grow greens such as lettuce.  He is not the first to have done this, in fact a team in Taiwan had been testing this already, but somehow he is the one that popularised it and hence it is now known as the Kratky method.

The kratky method

The great thing about this type of setup is that it is literally zero maintenance.  We have spent the last two months experimenting and perfecting a way to minimise the amount of effort required for each step of the process from seed germination to transplanting.  In the following posts I will focus on each of these and how we do it.