When we started learning about hydroponics this was one particular question we couldn’t get a straight answer on. Everyone we talked to had a different answer than the next guy, and sometimes those answers contradicted with each other! We’d like to take a moment to explain our position on the matter, and maybe better explain why people are so split as to which unit is better to use.

When you stick an EC/TDS probe into a hydroponic solution, all the sensor probe is really doing is measuring the resistance, or how easily electricity flows through the fluid. Pure water does not conduct electricity very well, but as you add synthetic salts as you would in a hydroponic application the electrical conductivity starts to increase. We use electrical conductivity to determine how much food our plants are being served. Very simply, the more nutrients in the reservoir, the more electrical conductivity you get.

So then when do EC (electrical conductivity) or ppm (parts per million) units come into play?

When you put your EC/TDS probe into your hydroponic solution we said it’s measuring resistance. Okay, then what does that have to do with conductivity? The EC/TDS meter is going to measure the resistance of the solution in Ohms (which is just a unit used to express electrical resistance). As resistance goes up, electrical conductivity goes down and vice versa. We call this an “inverse relationship,” and like the name implies all we have to do to calculate conductivity is take the inverse of resistance. So for instance, if our EC/TDS meter measured the solution as 500 Ohms, then it has to convert that value into conductivity:

Notice the “S” after the 0.002. That stands for “Siemens,” which is the unit used to represent electrical conductivity. You can see how simple it is to compute. The only caveat is that most people don’t run their nutrients strong enough to reach 1 Siemen (sea water isn’t even 1S) so they usually multiply the value by 1000 to get a less cumbersome number. When we do this we get 2.000mS, or two “milli-Siemens.” Multiply the number by 1000 again and you get 2000uS, or two thousand “micro-Siemens.” All are equally acceptable units used to express electrical conductivity, and hence nutrient concentration.

1 Siemen (S) = 1,000 milli-Siemens (mS) = 1,000,000 micro-Siemens (μS)

or

1 micro-Siemen (μS) = 0.001 milli-Siemens (mS) = 0.000001 Siemens (S)

So what about ppm? ppm stands for “parts per million” and actually has no direct relationship with electricity. People typically use ppm to quantify trace amounts of “stuff” within a volume of some “other stuff” that is otherwise pure. For example, if I had a million marbles and the concentration of white marbles was 1ppm, that just means for every 999,999 black marbles, I have one white one. Okay fine, so how does that relate to hydroponics?

Well, we established that the salts in nutrient solutions increases electrical conductivity as the concentration increases. The problem is that statement is too vague because different salts have different conduction properties!! So for instance, 1000 parts per million of table salt in water would have different electrical conductivity than say, 1000ppm of potassium chloride in water. This example shows one of the great downfalls of using ppm to express nutrient concentration: YOU MUST SPECIFY WHICH SALT YOU’RE MEASURING! If someone tells you to nute your res to some given ppm value, your next question should be, “ppm of what?”

In a nutshell, the problem with ppm is that it requires an extra and arguably useless conversion in order to calculate it, and this gets confusing for people. We already know how conductive our solution is, which is indicative of our nutrient concentration, and that’s what we actually care about. However, TDS meters add an extra step in there based on the assumption that you’re only interested in measuring one particular type of salt. Some meters are calibrated for sodium chloride (NaCl), and assume you’re running that. Other meters are calibrated for potassium chloride (KCl), and some meters are calibrated for 40% sodium sulfate, 40% sodium bicarbonate and 20% sodium chloride (442). To make matters worse, sometimes the type of salt a TDS meter is calibrated for isn’t plainly obvious. And sometimes nutrient companies don’t declare which ppm conversion value they expect you to use. And sometimes people refer to different conversion factors by the big companies that use them like, “The ‘Hanna’ conversion factor.” AHHHH!!!! This is way more trouble and confusion than it’s worth!

Let’s walk through an example to illustrate the point. A TDS meter is calibrated to measure the concentration of NaCl, which carries a conversion factor of 0.5. If the meter measures the nutrient solution to be 500 Ohms, what is the resulting ppm value?

Note above that all we did was calculate the electrical conductivity in micro-Siemens, and then we applied the conversion factor of 0.5 to get to ppm.

Okay, so what if the meter was calibrated for 442?

Again, all we did was calculate the electrical conductivity in micro-Siemens, and then applied the 442 conversion factor of 0.7.

Look, both measurements are represented in “ppm” but you can see the difference between the two is nearly 30 percent! All it takes is a vague nutrient product label or a poorly marked TDS meter to screw this conversion up and accidentally stress your plants. This is exactly why Grohaus Automation prefers to use electrical conductivity to express nutrient concentration. There’s only one type of electrical conductivity: Siemens. Unlike ppm, which can have several different interpretations and conversion factors, electrical conductivity is always the same no matter what type of salt you’re measuring. 1mS will always equal 1mS, no matter what you’re measuring.

So if measuring TDS is so terrible then why is it the industry standard in North America? The problem is cyclical like a mobius strip. Manufacturers use TDS because they think that’s what their customers want, and customers use TDS because that’s what the manufacturers use. The majority of growers in Europe know what’s up, and they use EC to represent nutrient concentration. If North American consumers made enough of a stink about how cumbersome it is to use TDS then the big manufacturers would probably change their convention. They want to make customers happy, after all.

Grohaus Automation is giving it’s own subtle push in the right direction. Our Hydroid control system’s user interface defaults to EC for all nutrient concentration measurements. You can of course change this to ppm (either 0.7 or 0.5 conversion factors), but we’re trying to get people used to looking at EC values. We feel strongly using EC will result in less feeding mistakes, but we also strongly believe in giving people options! So choose which one works best for YOU and stick with it.

Have an opinion on the matter? We’d love to hear your two cents! Head over to the Grohaus Automation forum and sound off…

Hydroid beta testing officially begins this week! This represents a quantum leap forward for us, and we’re so excited to start this new phase of our project.

Not sure what ‘beta testing’ is? Not to worry…

From Wikpedia:

“Beta testing comes after alpha testing and can be considered a form of external user acceptance testing. Versions of the software, known as beta versions, are released to a limited audience outside of the programming team. The software is released to groups of people so that further testing can ensure the product has few faults or bugs.”

Like the quote above says, we’re releasing the Hydroid automation system to a small group of people so we can get some feedback on the product. Over the last 6 months or so we’ve amassed literally tens of thousands of lines of code that govern the operation of the Hydroid, and now it’s time to methodically run through each and every line to make sure it all works as we expect it to. Since there are a dizzying number of functions and facets to test this beta evaluation really becomes a numbers game. The more people we have evaluating the system, the quicker we’ll get through this process and begin offering the Hydoid to the general public. We go through this process because if you can’t trust to leave your automation system alone for long periods of time, then really what good is it?

Let’s consider a hypothetical situation: You just bought brand XYZ automation system (be it a Hydroid or some other garden automation product) and it has been shown to be absolutely 100% reliable. That means you’ll never have any surprises in your grow room, right? That’s unfortunately far from the truth. Even if your automation system properly doses nutrients for your plants, runs your lights properly, and maintains the ambient conditions that are ideal for your garden, what happens if your nutrient pump fails? Will your automation system recognize this condition and alert you to the problem? For a moment, consider how many devices you absolutely rely on in your garden, and what could happen if one of those machines fail without anyone taking notice until it’s too late.

Thankfully the Hydroid can indirectly detect faults that could otherwise wreak serious havoc on your plants. This is because the Hydroid has the ability to accept both analog and digital inputs, which can be used as fault detectors. We could have easily eliminated this feature and released our product to market sooner, but this kind of versatility is absolutely indispensable for any good automation system. Here’s an example why.

Consider this scenario: You’ve spent thousands on your garden and bought all of the best equipment available…pumps, lights, fans…it’s all top of the line. You get everything set up and running, and when you least expect it your ballast fails. Under normal circumstances you wouldn’t be alerted to the failure until you walked back into your garden. If you leave your garden for long periods of time you can imagine how damaging it could be for your plants to sit in the dark like that. If losing a crop is disastrous, how about a serious fire or flood?

In the case of the light dying, if you had a light meter attached to the Hydroid it would be able to monitor the light output of your bulb. If the ballast were to fail then the Hydroid can be programmed to text or email you notifying you of the situation. In the case of fires or floods, the end-user may connect a fire or flood sensor to the Hydroid and it’ll notify the user if either of those sensors are tripped. The sky is the limit though. You can attach sensors that can detect is pumps, fans, lights, or any other devices fail, or anything else you want to monitor. This ability to immediately report problems can be an incredibly powerful safety service if you do leave your garden for long periods of time.

The name of the game in garden automation really is reliability and dependability, and we’re working hard to ensure that our customers get a product that they can rely on. In the coming weeks we’ll do our best to update everyone on our progress, and in the mean time please feel free to contact us for more information about our Hydroid automation system. And thanks for checking us out!

As you can see the software can accommodate nearly any kind of growroom device, conditions, or hydroponic setup. We tried very hard to make it as flexible as possible without becoming overwhelming. If you have any questions about your particular setup, and whether the Hydroid can support it please contact us so we can discuss your requirements.

You can think of the Hydroid as performing two major functions in your garden: It feeds your plants as necessary, and it will intelligently control any devices that you use in your grow area. So everything you see here is designed to serve those two purposes. Let’s take a closer look at how the nutrient doser works first.

The heart of the Hydroid system is the enclosure containing the nutrient dosing equipment. It utilizes a pneumatic injection system, relying on compressed air to push nutrients into a hydroponic system. The system does not rely on gravity in order to deliver nutrients.

The 1-gallon nutrient containers you see inside are made from high density polyethylene. They were custom made for our product, which means they’re designed specifically for use with hydroponic solutions such as pH modifiers and concentrated nutrients. No need for dilution here.

You can also see the white and black solenoid valves scattered along the base of the system. These electronic valves control the flow of nutrients through the delivery lines. When the computer determines that your plants are hungry each solenoid valve opens for a period of time proportional to your specified nutrient ratio.

The gold colored item in the picture is the air compressor. This is used to maintain pressure within the nutrient containers. If the Hydroid didn’t use an air compressor the alternative would be gravity feeding, which requires placing potentially heavy fluid containers up in the air. Not only can this be dangerous, but it also doesn’t provide consistent flow through the nutrient lines as the water level drops. The tanks are maintained at 10psi during injection events, and a relief valve vents the pressure once the nutrient dosing is complete.

Also note the green circuit board hiding in the back of the Hydroid. This is the brain of the system, and this is also where the majority of devices are connected. More on this in a minute.

Finally, note the bulkhead connectors on the side wall of the Hydroid. All connectors utilize polypropylene seals which means they’re safe for whatever hydroponic chemicals you wish to use. The outlet of each solenoid goes to one of these bulkhead connectors, and ultimately ends up somewhere in your hydroponic system. We include 50 feet of tubing so there should be plenty of flexibility in running nutrient lines.

In the third picture we have the complete Hydroid system sitting in front of our drink dispenser. The drink dispenser uses the exact same hardware as the Hydroid nutrient doser, but instead of dispensing nutrients it dispenses mixed drinks! We brought it to the Maximum Yield Indoor Gardening Expo and thought it would be a cool way to demonstrate our injection system.

But here you can get a sense of scale for everything, and you can see everything that comes with the Hydroid. From left to right you have the SensorBox, which houses all of the atmospheric sensing equipment (more on that in a minute). Next to that you can see the 10″ touch-screen tablet computer. This what we recommend people use to interface with the Hydroid. The software is formatted for a 1024×600 resolution screen, and the touch interface is almost identical to interfacing with your favorite smart phone…no keyboard or mouse required.

It’s difficult to see in the picture, but next is the pH and EC probes. Both probes are laboratory grade, and because we use custom designed pH and EC circuits you’ll never pickup any unwanted RF interference from your digital ballasts. We went through great lengths to ensure that the sensing is impervious to RF noise.

Lastly we have the AuxBox. The AuxBox is what the Hydroid uses to turn devices on and off. You can think of it simply as a relay in a box. You plug your device into the Auxbox, the AuxBox power into the wall, and the RJ45 plug goes into the Hydroid. You can then program the Hydroid to turn your device on and off relative to whatever process you choose. Want your exhaust fans to turn off when your CO2 generator turns on? No problem. Want to turn on a dehumidifier when your relative humidity gets too high? Again, no sweat. These boxes are really powerful when used in conjunction with our control software as you can control nearly anything you want.

Let’s get back to the SensorBox for a moment. The SensorBox is used to sample the ambient conditions in your garden. It uses an infra-red CO2 sensor to measure carbon dioxide concentration, and also samples the ambient temperature and humidity. The data cable we use is fine being run over long distances, so there’s a lot of flexibility as to where you can put it. Not to mention, it does have a small fan inside which helps move air over the sensors inside.

Lastly, we wanted to point out the hookups on the back of the Hydroid. Some of them are pretty self-explanatory, but a few of the connectors towards the bottom may need some detail.

Tank expansion is exactly as it sounds: If you need more tanks, you can hook up another five to the standard five that come with the Hydroid for a total of ten.

Below that you have some alarm inputs and outputs. So what are those good for? Alarm inputs can be used to connect devices that sense problems in your grow room. For instance, if you leave your space for long periods of time you can connect flood or smoke detectors. If there is a problem you can have the Hydroid send you a text or email when the alarm is tripped. But the sky is the limit. You can hook anything up to the alarm input so long as it acts like a switch. So, glass break sensors, motion detectors, chemical sensors…whatever you wish. The alarm outputs work the other way around. Instead of the alarm telling the Hydoid there’s a problem, the alarm output is designed to drive any 12-volt device like a siren for instance. You can program the software to turn the alarm output on when a particular sensor goes outside a range you specify.

Analog input is actually just a generic input. If you want to measure a sensor that we don’t already include and monitor, you can hook it up here. It’ll accept just about any 0-5-volt analog sensor. So for instance, maybe you want to monitor the moisture content in your drain to waste system. Or maybe you want to datalog the PAR output of your lights over time. We’re sure our customers will dream up ideas that we never even thought of.

So that’s a brief rundown of the Hydroid. If you have any questions about the information presented here please use the comments form below, or feel free to contact us. We appreciate everyone’s comments and feedback. Thanks for checking us out!