Frequently Asked Questions about Hydroponics - 2019
This tutorial is a revised and updated version of our FAQ about Hydroponics
What is Electrical Conductivity?
Electrical conductivity or EC as it relates to hydroponics is a measure of the dissolved salt content in any given aqueous solution.
To put it more simply EC indicates how the strength of any given nutrient mix you have made up. The more nutrient you add to your mix the higher the EC will be.
EC is the primary measurement used in assessing how much nutrient to give a plant at any given point in its life cycle. As plants grow they require more nutrition to stay strong and healthy, young plants will usually require an EC of between 0.2 and 1.0 where as fully mature flowering plants may require an EC of between 2.0 – 3.0.
For horticultural purposes EC is the most accurate way to measure the concentration of nutrients in your mix however there are other units of measurement relating to this, these are Parts Per Million (PPM), Total Dissolved Solid (TDS) and Concentration Factor (CF).
What is pH?
Potential Hydrogen or PH is a measure of how acidic or alkaline any given liquid is.
Understanding and managing the PH of your nutrient mix is extremely important when growing hydroponically. The PH scale ranges from 0 to 14 where 0 is the most acidic, 14 is the most alkaline and 7 is neutral. Pure water has a PH of 7 whereas lemon juice which is acidic has a PH of around 2 and bleach which is alkaline has a PH of 12.
PH becomes important for hydroponic growers when we start thinking about feeding our plants, as we add different nutrients to our water these nutrients will have an effect on the PH of the mix, some nutrients will raise the PH and others will lower it, the key is once we have everything mixed up and we have ensured our EC is correct we then need to check our PH and adjust it if necessary.
PH is easily adjusted by using a ‘PH Up’ or PH Down’ solution sold at all good hydroponics stores. All plants have a preferred PH range that will ensure healthy vigorous growth, most plants like a slightly acidic range of between 5.5 and 6.5. If the PH of your solution falls out of the required range then the plant will be unable to take up and use key elements from the nutrient solution and thus deficiencies or toxicities will soon appear.
There are some very helpful videos online for those growers interested in learning about the chemical processes behind PH and PH changes however provided a grower knows their plants desired PH range and has the ability to measure and adjust the PH of their nutrient solution everything should be AOK.
What EC should I maintain?
EC (Electrical conductivity) requirements change as the plant grows from seedling into a mature plant. When your plants are young they require less food, so it makes sense that as the plant grows we increase the amount of food to fulfil the plant’s needs.
Seedling requirements: 0.4 – 0.6
Growth/Vegetative requirements: 0.6 – 1.6 EC
Bloom/Flowering requirements: 1.6 - 2.4 EC
What pH should I maintain?
The consensus for pH in a hydroponic system & coco coir is that it should be kept between 5.5 - 6.5 throughout the cycle, ideally in the growth/vegetative phase pH should be maintained at 5.8-6.2 - if the pH fluctuates too much the plant will be unable to uptake specific nutrients, so having the necessary equipment like a pH pen will save a lot of guess work.
When the plants go into the flowering phase consistency is key ensuring the plant has a constant supply of the nutrients it requires, the preferred range in flower is 6.0 - 6.4 as different elements are required in the bloom phase, if this range was lower or higher the plant would be unable to absorb targeted nutrients, thus stifling development and severely impacting the end result.
How long should I run my lights?
The general rule of thumb for vegetating plants is 18 hours of light and 6 hours of darkness, once flowering has begun or the plant is of suitable size to flower you will need to change your photoperiod to 12 hours on and 12 hours off, keeping in mind that once your plants start flowering the darkness cannot be interrupted, if light enters the space when flowering, you could reset the plant to vegetate or even worse, they can mutate which will massively impact the end result. It is not recommended that plants receive 24 hours of continuous light at any time during the life cycle. Many growers will leave their lights off for the final 36-48 hours of their grow to great results.
Does the nutrient solution need to be heated?
For optimum growth, it is best to maintain your nutrient solution at a temperature of between 18 – 22 degrees (C)
If the room temperature falls below 17 degrees during the dark period, then you will require a water heater. If the nutrient solution does go below 18 the plant can stop growing and go into shock.
If the solution is above 22 for too long it can become the perfect breeding ground for algae, Pythium and a host of other bacterial infections
What causes plants to die?
There can be a number of reasons for this. Firstly, eliminate the obvious things like lack of water, high temperature or a broken stem.
Root diseases are the most common cause of "sudden death" for plants and can cause many problems from loss of yield to complete death. Pythium is the most common disease. Ignoring the basics on temperature control can present quite a nightmare. Always use nutrient conditioners if you reservoir is prone to temperature rises, these formulations mostly contain quaternary ammonium and copper which will help prevent nasty pathogens from taking hold.
What causes the tips of the plant’s leaves to burn?
This is usually caused by overfeeding i.e. giving your plants too high an EC before they are ready for it. It can also be caused by a buildup of salts/food within your growing medium. If you suspect either of these scenarios it’s a good idea to fully flush your plant then go in with a reduced EC.
There are some nutrient deficiencies that can also cause leaf tip burn. Again, if the gardener has themselves a pH and EC meter this is rarely an issue.
What causes leaves to turn yellow?
This can be caused by a number of factors:
- Low oxygen levels due to lack of aeration or too much water.
- A nutrient deficiency.
- The pH is too high/low.
- The solution is too hot/cold.
- EC too high/low
All of these prevent the plant from absorbing nutrients in the correct quantities, always use an EC meter and a pH pen to prevent this from happening. It should be noted that towards the end of the flowering cycle it is normal for the lower leaves on the plant to start turning yellow.
Why do plants stretch?
Plants stretch when their light source is insufficient, humidity is too high or they are crowded by other plants.
Lowering or turning up your light, increasing air flow or spacing plants further apart are some good options.
It should be noted that for 14-21 days after the lights are changed to a 12/12 cycle your plants may ‘stretch’. This is more referring a period of further vigorous vegetative growth and should be anticipated.
What Humidity (RH) should I maintain?
Excessive humidity for long periods will create undesirable conditions that are perfect for grey mould to thrive. Grey mould, once started, will quickly spread and affect your entire crop.
Using a hygrometer device mounted on the wall inside your hydroponic grow room will let you know at a quick glance what your humidity levels are. Humidity levels of just above 50% during flower is perfect and should not go above this. It is important to keep nutrient reservoirs covered at all times so that they do not contribute to higher humidity levels.
Humidity levels can be easily controlled as with temperature by using inlet & extractor fans to rid the room of heat or humidity. Generally, it is good to keep your grow rooms clean and dry. This will help prevent any mould problems.
What Temp should the growing room be?
While the lights are on temperatures should be maintained between 22 and 28 degrees. When the lights are off temperatures are permitted to drop by 5 degrees or so. It is best to avoid large temperature fluctuations in the growing space at all times. If temperatures fall outside the optimum range for too long development can be significantly stifled or worse. Your main tool for regulating temperature and humidity in the grow room will be a quality exhaust fan.
How much ventilation is necessary?
The main purpose of ventilation in a grow room is to expel hot and humid air and to replenish CO2. Finding the perfect balance between optimum temperature, humidity and CO2 can be tricky and thus investing in the right gear from the start is important. A good quality variable speed extractor fan will serve you well. As a general rule, you want an extractor fan that can complete a total exchange of vapour within the grow room every 1 – 3 minutes.
Should I use EC & pH meters?
Operating a hydroponics system without meters is very difficult and it would be very hard to achieve optimum results. Always use meters to attain perfection.
What size reservoir should I run?
Depending on the type of system you are running and the plants feeding requirements.
For ease of control use a minimum of 45 ltrs per/m2 of growing area, less than this requires frequent adjustments.
Some systems like DWC (Deep water culture) actually have the plants growing in a large volume of water and nutrients, this type of system can be plumbed to an external reservoir that will top up your main system as the solution depletes.
Is it necessary to aerate the nutrient solution?
Aerating the nutrient solution is a good idea. It guards against stagnant water, improves plant health and prevents bacterial infections. Aerating a nutrient solution will last far longer than one that is sitting flat. Generally speaking, if you are running a recirculating hydroponic system or intend to store a nutrient solution for more than 24 hours you should be aerating your nutrient solution.
How long should it take for clones to strike roots?
The time taken to strike roots on clones varies according to the time of the year and the health of the clones and whether the method is manual or assisted About 5-12 days is usual for most manual methods.
Assisted methods include cloning machines that drastically speed up oxygen intake which in turn can force roots to form with 3-7 days.
What is the best water to use?
The best water will have low salts or contaminants. Rainwater is probably best though normal tap water is usually satisfactory and convenient as long as it is under 0.3 EC
Most Australian tap water is valued between 0.0 - 0.3
Reverse osmosis is fast becoming a preferred method as well, the only downside is pH fluctuations (using a pH stabiliser will correct this) and the water after it is cleaned will require re-conditioning with a calcium magnesium additive.
Which type of grow light should I use?
The choice of light used in your grow room will arguably be your most important decision when setting your space. There are several lighting options to consider when building a hydroponics set up. All options have their pros and cons and these should be considered carefully before making your decision.
The most common choices are High Intensity Discharge (HID), Light Emitting Diodes (LED) and Florescent lighting.
HID lights are the most common grow light used they have been the industry standard for decades now and as a result the price of these lights has become very affordable. They have shown to give gardeners consistent results over the decades when used correctly.
The down side to this option is the colour spectrum for HID lights are quite limited thus you will need to use two separate lamps (globes) for different stages of growth.
During the vegetive stage it is best to use a Metal Halide HID Lamp and then for the bloom stage it is advised to use High Pressure Sodium lamp these lamps should be swapped out for new lamps every 6-12 months.
Often another down side to this option is HID lights run very hot therefor it can be difficult to control temperatures in your growing space. If temperatures exceed 29 degrees in a grow room it can severely affect the quality of the finished product.
A promising new evolution in the HID market has been Light Emitting Ceramic (LEC) fixtures also known as Ceramic Metal Halide (CMH). These new HID lights offer the plants a full light spectrum and run more efficiently than older HID options.
The down sides to these lights are they still produce a lot of heat and they can not be powered by traditional HID ballasts as they require specific low frequency ballasts to operate.
LED grow light fixtures are becoming more and more common and can offer growers very impressive results due to their wide range in colour spectrums and incredibly efficient energy use.
Unfortunately, due to a large amount of cheap, sub-par LED grow light models flooding the market over the last 5 or so years the true potential of LEDs hasn’t been fully realized by gardeners.
As LED technology improves and the market becomes more savvy there are more companies offering high quality and extremely powerful LED fixtures for all types horticulture.
The efficiency of LED fixtures comes primarily from the fact that almost all the power used by the fixture is converted into light energy as opposed to heat energy which is a huge benefit for growers in warmer climates however growers in cooler climates will have to supplement with heaters.
High quality LED fixtures have the additional advantage of maintaining the same level of light output for up to 10 years.
Fluorescent lighting is a relatively efficient full spectrum lighting option that works best for gardeners raising seedlings, clones and looking after mother plants. These fixtures usually range between 50w and 200w and as such aren’t a great option for later vegetive and flowering growth but will provide young plants with the full spectrum and warmth they require to thrive before being put under a HID or LED fixture.