Hydroponic Reservoir Management
How To Monitor & Manage Hydroponic Reservoirs
Good hydroponic reservoir management is key to achieving the full potential of your hydroponic growing system. The reservoir or nutrient cistern in a greenhouse or indoor farming operation acts like a heart, circulating oxygen and nutrient rich solutions to thirsty roots for absorption. In the case of recirculating reservoir or RDWC system, the solution may also be returned and recirculated to conserve water and make for higher fertilizer use efficiency.
Let’s discuss some foundational pillars for developing healthy and productive hydroponic reservoir management practices. Don’t worry, you will not have to spend your time chained to your reservoir; technology and knowhow will make your life easier and add to the bottom line.
It would be presumptuous to overlook this area. Ensure that all the plumbing parts, pumps, pipes, float valves, fittings and reservoir construction are made from suitable materials such as ABS, PVC, fibreglass or stainless steel. These are inert materials, meaning they won’t react adversely with your nutrient solution, which by the way, is a mildly acid and saline solution. Copper, brass and some types of plastic may not play nicely with hydroponic nutrient solution, leeching metals into solution that can harm or even kill your crop. If you are buying a complete system from a reputable growing solutions provider this isn’t something you will typically need to worry about.
Nutrient Solution Capacity
In drain to waste systems, the capacity of the reservoir tends to be lower–as it is replenished often with fresh water, nutrients, additives, pH buffers, etc. Because the water is not recirculating in drain to waste systems, growers usually don’t want the tank getting “stale” and may only have enough nutrient solution for one to two days.
In recirculating hydroponic systems and RDWC systems, the volume of solution tends to be higher to buffer against changes in EC, pH, ORP, etc as plants take up water and nutrients. Note, this doesn’t mean recirculating hydroponic systems use more water–to the contrary, they often use less. Think of the weekly volumes versus daily. A crop occupying a 20′ X 60′ room with HID lighting and Carbon Dioxide Enrichment will typically require a volume of 600 US gallons (roughly half a gallon per square foot for fill volume, excluding top ups).
Nutrient Change-Out Frequency
In theory, you don’t have to change the volume of nutrient solution through the entire bloom cycle–just manage it very carefully with additions of water, nutrients and additives. However, in practice this isn’t usually easy and doesn’t deliver the best results. Besides taking up water and nutrients, plants also exude wastes through their roots. Additionally, roots grow and die back through the life of the crop to an extent; very much like our skin. Not removing these naturally occurring plant wastes can lead to issues in recirculating hydroponic systems.
So, changing the nutrient solution once a week in bloom, typically by 25 to 50% of the total solution volume in the system, and every few weeks in veg has benefits. Besides removing plant wastes from the system and reducing the microbial load nutrient change outs allow growers to “update” the crop diet to address the specific needs of each week of development. A well formulated feeding program yields better quality and more of it versus trying a one size fits all approach to crop nutrition.
Naturally, the water quality you add to the system counts–it’s a very important area. For a more in depth look at hydroponic water management Click Here.
Hydroponic Reservoir Management Practices
Add Back for EC
When EC levels lower from the target concentration, nutrients should be replenished for optimal crop performance. If not, imbalances and deficiencies can occur over time between weekly nutrient change outs. Larger and sophisticated indoor farmers may use dosing systems to achieve desired levels automatically and in controlled mappable quantities and ratios.
Growers may use a manual approach with good success by adding desirable ratios and values–i.e. following the feed program, nutrients and additives are added to the system to reacquire the target values after crop uptake. Note that allowing the nutrient concentration to drift within a range is acceptable. For additional feeding recommendations contact firstname.lastname@example.org
CCH2O’s Add Back Kit allows the flow of recirculating nutrient solution to draw up diluted concentrates and slowly add them into the system, preventing potential shock or drastic change to the rhizosphere.
The Oxidative Reduction Potential of a nutrient solution is a measure of the health of your nutrient solution where roots are concerned. A low ORP value suggests stagnation, anaerobic bioactivity, decay–none of the things that are desirable for healthy hydroponic crops.
Good recirculation and aeration help to keep ORP levels near the powerband (250-350mV) for optimal crop health in the root zone. Adding hypochlorous acid (ClearLine, UC Roots) to systems and reservoirs daily, as directed, is an excellent way to keep ORP levels up while directly combating biofilms, salt build-up, etc that can occur in recirculating hydroponic systems.
As most growers are aware, maintaining the correct pH for your crop type and growth stage in a given hydroponic system is vital to ensure maximum water and nutrient uptake by plants. Free pouring pH adjusters into the reservoir has been a common practice based on daily checks and monitoring, however, is not the best method. Real time monitors and dosing systems can keep the pH in the optimal range 24/7, preventing hiccups in potential nutrient uptake by the crop on a daily basis.
If adding pH adjusters manually, the add back method (as with EC, above) is a considerable improvement over pouring concentrates directly into systems or reservoirs for better hydroponic reservoir management. Most hydroponic crops will thrive in a pH range from 5.8 to 6.3. Maintaining a constant pH value is easier to accomplish with a doser. However, many growers prefer to allow their crops drift through the optimal range before adjustment as different minerals will have greater availability at different pH ranges.
Chilling Hydroponic Systems
Keeping the temperature of the nutrient solution and root zone is vital for maximum crop production and plant health. If nutrient solutions overheat they cannot hold high levels of oxygen when large root masses are present.
Conditions can become anaerobic, hurting growth potential and inviting problems. Typically, the optimal temperature (65-68 Deg F) in the root zone is cooler than that of the air temperature for the plant canopy. This means active cooling practices may be required. Click Here to learn more about chilling hydroponic systems.