Please note, all EC to PPM figures quoted below use a conversion factor of 0.5.
TDS – ( PPM / EC NUTRIENT STRENGTH MONITORING ) Along with pH, nutrient strength readings and monitoring are probably the 2 most important basic techniques you can employ in your chase for the best crop possible.
Whereas pH monitors the acidity or alkalinity of a solution, TDS ( Total Dissolved Solids ) measures the relative concentration / strength of nutrient salts in your nutrient solution. TDS – or Total Dissolved Solids normally uses 1 of 2 scales, PPM ( Parts Per Million ) or EC ( Electro-Conductivity ). Both scales are accurate and convenient for monitoring the strength or concentration of your nutrient solution.
WHY IS IT IMPORTANT TO MONITOR THE STRENGTH OF YOUR NUTRIENT SOLUTION? I like to think of pH and TDS readings as a kind of dashboard for my plants performance. TDS is like the tachometer on your car. It tells you how far or fast you’re pushing your plants with a nutrient solution. Plants respond to TDS just like a car does in real life to a tachometer. The higher the revs, the faster the car accelerates, BUT, if you push your cars revs into the red zone for too long bad things start to happen - FAST! It’s the same thing with plants. Having a higher nutrient strength results in faster growth and development - but only up to a point – go past your plants red line and into the red zone and bad things start to happen – really fast!
SO WHERE IS MY PLANTS REDLINE? HOW HIGH CAN MY NUTRIENT SOLUTION GO? The optimal nutrient strength for your plants will depend on 3 things – the age of your plant, the type of plant and individual variations amongst plants.
For example most older ( more than 4 weeks old ) fast growing plants can safely handle nutrient strengths up to 1200 PPM ( 2.4 EC ) once they are past the seedling or juvenile stage. Some individual plants can handle much higher concentrations than this - up to and over 2000 PPM ( 4.0 EC )!
The other way to get your plants to safely handle larger amounts of nutrients is to use a 3rd generation nutrient that incorporates ionic channelling technologies, such as Dutch Master GOLD NUTRIENT. These technologies allow for a typical plant to handle much higher nutrient strengths than normal. A plant that could handle only 1200 PPM ( 2.4 EC ) on a regular nutrient can easily handle 1600 PPM ( 3.2 EC ) with an ionic channelled nutrient like Dutch Master GOLD. Currently only Dutch Master GOLD NUTRIENT has this ionic channel technology.
The best way to tell if you have reached your plants maximum nutrient concentration ( the red line ) is when you start seeing the very tip of your leaves turn brown or yellow. This often looks like a small burn ( which it is ). Once you see this you know you have reached your plants maximal nutrient strength.
Once you know your plants red line or nutrient strength limit, it is a good rule of thumb to not let the nutrient concentration get more than 150 – 200 PPM beyond this ( 0.3 – 0.4 EC ).
HOW DO I MONITOR MY NUTRIENT STRENGTH AND WHAT DO I DO WHEN IT CHANGES? Monitoring your nutrient strength is easy as many manufacturers give you precise schedule values for their nutrients. Dutch Master has made this easy for you with the industry’s easiest and most powerful Nutrient Calculator! Simply enter your tank size and your base nutrient and the calculator does all the rest! It really is that easy!
Monitoring your nutrient strength should be done on a daily basis for hydroponic systems as your nutrient strength can tell you a lot about what is happening with your plants. As your plants use water or food, your nutrient strength will change to reflect that. When your plant is using a lot more water than nutrient then your TDS value will increase. When your plant is using a lot more food than water then your TDS value will go down.
Mostly these values fluctuate ( go up and down ) by not more than 100 to 150 PPM ( 0.2 to 0.3 EC ) however when they do, you need to take action. If your solution ( or runoff values for hand watering ) changes by more than 150 to 200PPM ( 0.3 to 0.4 EC ) then you need to either replace the solution in your reservoir, or replace the nutrient solution in your reservoir and perform a flush. Typically you will need to do the latter as nutrient solutions tend to rise over time.
HOW DO I PERFORM A FLUSH IF MY PPM / EC IS TOO HIGH? Performing a flush is an easy task to do. You simply run your preferred flush solution, pH adjusted, through your system and monitor the runoff of this solution returning to the reservoir or out of the bottom of your pot. Keep running the flush solution until that runoff or return solution is approximately the same TDS ( PPM / EC ) value as your pH adjusted flush solution. After your flush is completed simply dump your flushing solution and make up a new full strength reservoir as per your feed schedule or nutrient calculator recommendations.
MAKING SURE YOUR NUTRIENT METER IS ACCURATE IS VERY IMPORTANT! Now that we know the basics of monitoring and taking corrective action based on our nutrient strength readings, we must also learn about one vital aspect.
I have seen more people kill their plants or cause major problems with an incorrectly calibrated TDS meter than almost anything. As much as a TDS meter gives you power over your plants, an incorrectly calibrated one can cause a lot of problems. The most common but least understood problem is battery voltage. A meters battery will slowly lose charge as the meter is used over time - pretty straight forward, right? Wrong! Once the meters battery loses voltage past a certain point, it begins to affect the meters readings in a negative way. As the battery voltage lowers so too will the meters readings. Quite often this reading will be many hundreds of PPM’s lower than what the real reading is. End result? Quite often people will severely over feed their plants and when they burn, who gets the blame? The poor old nutrient manufacturers! Your meter should be calibrated weekly and the battery changed every month or the first time you notice that you have to calibrate your meter up when using your calibration solution
HOW DO I CARE FOR MY METER? Calibration and care of your TDS meter is vital if you are to get accurate readings. An incorrectly calibrated or poorly maintained TDS meter can cause as many, if not more, problems as using no meter at all! Calibrating and maintaining your TDS meter is simple and takes virtually no time at all! For greatest accuracy calibrate your meter at least weekly in a good quality calibration solution. Make sure that you purchase a calibration solution that is applicable to your meter. Meters using the PPM scale should use a PPM calibration solution and meters using EC should use an EC calibration solution. Try and obtain a calibration solution that is close to the median range of your feeding solution. This is normally between 1000 and 1400 PPM ( 2.0 to 2.8 EC ).
Also ensure that the probes of your TDS meter are clean. You can purchase TDS probe cleaning solution from your local hydroponics store. A good rule of thumb is to clean your probes just before you calibrate your meter.