10 Things to Know About Your Nutrient Reservoir

By Sara Elliott
Published: February 20, 2017 | Last updated: April 27, 2021 12:55:14
Key Takeaways

Though many other technical aspects of a hydroponic setup get all the attention and star billing, the nutrient reservoir assembly can be considered the heart of your system—and is vitally important. It pumps fluids to waiting plant roots, and a reservoir failure can result in disaster. Sara Elliot explains why that box or barrel of water holding a precious cargo of mineral salts deserves your respect and attention.

Let's take a look at 10 things you should consider when pondering the efficacy of your nutrient reservoir and system. Some of your persistent problems may begin, and could end, there.


Constructing Your Nutrient Reservoir

Reservoir fabrication is often a do-it-yourself project. Sometimes this is the most creative solution for a unique setup, but often it's a simple cost-saving measure. A large storage tote is one of the most popular choices for a starter reservoir.

Plastic storage totes for hydroponic water storagePlastic storage bins can be a good, inexpensive source for water storage but they can pose some problems. Source: Mike Flippo/Shutterstock


Totes are easy to source, inexpensive, and can accommodate enough water to make them a worthwhile option. Once filled, there can be problems, though. What looks like a thick and rigid enough wall to retain its shape under pressure can distort by bowing outward, either at first or over time when exposed to the warm conditions under hot lights. This can cause leaks around fittings and make it difficult or impossible to attach a lid.

Instead, choose a container designed especially for a hydroponic system, or one made using a heavy-duty, food-grade material, like a large picnic cooler or a barrel designed for food industry applications. Polyethylene (HDPE, LDPE) is a popular plastic used in these types of products. Although other plastics may work, they could also leach chemicals into the nutrient mixture or off-gas volatile organic compounds into your grow room or tent. The problem with making questionable choices is that problems won't necessarily present right away, and can be hard to pinpoint later.

Variety of water reservoir sizesThere are a variety of nutrient reservoir sizes to best suit your plants. Source: AlexLMX/Shutterstock


Choosing the Size of Your Nutrient Reservoir

It can be easy for hydroponic beginners to underestimate the size of the reservoir needed to raise plants to maturity. Plants need increasingly more nutrient as they grow from seedlings into large, healthy specimens. However, an educated guess can be made based on anticipated gallons consumed per plant at maturity, and the reservoir can then be sized accordingly.

A good general rule is that each large plant, like a tomato, will require three gallons of water volume. For a medium-sized plant, that drops to one-and-a-half gallons, and a small plant will require a half-gallon or so. Be generous if possible. For example, if you are planning to maintain four large, four medium-sized, and four small plants, your reservoir should hold at least 20 gallons to accommodate their needs.


As a cushion, doubling that capacity to 40 gallons isn't too generous. In this instance, more is better. A big fudge factor has built-in growth potential for more plants, and can sometimes save you the chore of adding nutrient as often—features you'll likely appreciate in the months and years to come.

If your setup can backfill into your reservoir during a power or other failure, make sure the tank is large enough to contain the volume of nutrient/water running through your entire system. Don't rely on a 40-gallon reservoir to hold 45 gallons in an emergency. If you do, you'll be disappointed, and probably spend hours mopping up the mess.

Large plastic water tanksMake sure the tank is large enough to contain the volume of nutrient/water running through your entire system. Be generous if possible. Source: jeffy11390/Shutterstock

Choosing the Right Location

If the design of your system doesn't require a specific tank placement, the first inclination is to place the reservoir as close to the action as possible, but that's not always the best choice. Where you put your reservoir can have an impact on how maintenance-intensive or headache-free its operations are. Once in place, the reservoir and its pipes, snaking hoses and accessories can be difficult to dismantle and move, so a little forethought is worth the effort.

Here are a few examples: If the reservoir is too close to your hot lights, then temperature fluctuations and algae can quickly become maintenance issues. The former may require the addition of an expensive chiller, while the latter can cause blockages and other headaches. Hotter water can hold less dissolved oxygen, too. If the reservoir is too far from a water source or drain, you may find yourself in the unenviable position of having to drag hoses or carry buckets around regularly.

Read also: Algae and Hydroponics

If the reservoir is placed too close to an uninsulated wall or concrete floor where temperatures plummet in winter, your mixture may fall below the optimum temperature range between 68 and 72°F and require the addition of a dedicated immersible or aquarium-style heater.

Also, if you're planning to add automation equipment, easy access to adequate electrical service is important, too. Adequate is important because a single circuit, often spread over several outlets, can only take so much current before flipping a breaker or blowing a fuse. Note: Check your electrical box. For quick reference, a 15A circuit can handle up to 1,800W, and a 20A circuit can handle 2,400W.

Checking pH value of water bin of hydroponics systemChecking pH value of water bin of hydroponics system. Source: rukawajung/Shutterstock

And the Tool You'll Need

You may be familiar with the manual testing tools you'll need to maintain viable nutrients in your reservoir, including meters that test for temperature, pH and TDS/PPM EC. If your system isn't automated, no meter or tool can earn its keep if you don't use it regularly.

To this end, multi-function or three-(four, five, or six)-in-one tools are widely considered the way to go. They save time and effort, and may even store previous readings for easy review and notation later. If possible, look for equipment that can be calibrated manually. This helps keep tools accurate over time and reduces the chance of equipment or operator error.

Read also: Understanding EC, TDS and PPM

Promoting Good Aeration

Dissolved oxygen in water is important for plant health. One way to achieve this in a nutrient tank is to continuously aerate the mixture. In recent years, the advantages of making adequate and even extra oxygen available to plant roots have been brought into sharper focus through the growing popularity of aeroponic and fogponic technologies.

Good aeration promotes nutrient uptake, sometimes dramatically, and aids in the growth of beneficial organisms. It also discourages the development of pathogens in the form of anaerobic bacteria. Adding one or more air stones or other bubble-producing devices to your nutrient tank is a form of extra insurance against shortfalls.

Another benefit of amping up the oxygen content of your mixture is that aeration keeps the liquid in motion and blended. It also helps maintain a consistent temperature and discourages algae growth.

Topping off Your Nutrient Reservoir

After you brush up on your chemistry, start blending nutrients and additives and combine them with prepared water. Wait, test, wait, test, and get your system up and running slowly—either again or for the very first time. It won't take long to notice the nutrient level in the tank dropping as the system stabilizes and plants take up water and transpire water vapor through their leaves.

There will also be moisture loss due to evaporation. More water is consumed or lost than nutrients, though, so water should be added back until you decide the remaining nutrient concentration is too low and should be augmented, or is just unreliable and should be replaced.

Make a note of the high-water mark in your tank, and check the level daily. Refill to that mark when topping off is necessary. You'll typically top off every few days depending on your setup, the type of plants you're growing and the temperature or time of year. Record how much water you're adding during each top-off session. This may help you determine when a change-out is due.

Some growers like having a second tank orbarrel of prepared water on hand. This can save time and reduce the risk of plant shock from the tap, well or other untreated water.

Flushing your hydroponic system regularly prevents issues down the road such as bacterial problemssFlushing your hydroponic system regularly prevents issues down the road such as bacterial problems. Source: Boophuket/Shutterstock

Flushing (Nutrient Replacement)

No nutrient recipe or delivery system is perfect, so problems do occur. Flushing a hydroponic setup regularly, including the entire contents of the nutrient tank, is important. The most common reason to flush a system and start fresh are chemical imbalances, which develop over time, but there are others.

The presence of clogging debris from seedling pots, root zone lockout, bacterial problems, or changing from vegetative growth to blooming are some examples of other conditions that may necessitate flushing. The best schedule for flushing is a matter of opinion, and often of lively debate.

Read also: Is Chemical Flushing Necessary?

The nutrient industry does a fine job of offering a wide range of targeted nutrient products. A new batch of nutrients, even with a variety of additives, will likely perform as advertised if prepared properly. So, how do imbalances happen?

Plants utilize individual mineral salts in nutrients in unequal quantities, depending on their needs at the time. Once introduced into the system, the mix is also exposed to environmental factors that can make specific minerals more or less available, including pH fluctuations, media interactions, and temperature variations. Over time, a carefully blended plant food becomes less and less reliable.

Beyond testing for the total concentration of dissolved solids in the water, it's hard if not impossible to know the composition of the mixture after a few days or weeks. Third-party testing labs can help, but their services are expensive. The safest choice is to flush often because this involves the least amount of risk to your plants.

Read also: Hydroponic Lab Analysis Tests and How to Use Them

Advocates of frequent flushing recommend monthly, bi-weekly, or even weekly schedules, especially for food or medicinal crops like vegetables and herbs that can take up residual mineral salts that may adversely affect their taste or wholesomeness. Frequent flushing of small systems is a good precaution, as adverse fluctuations present more rapidly in small systems than they do in larger ones.

There's merit in taking the safest approach in the beginning, and then experimenting with other options after you've established a baseline.

farmer monitoring the hydroponic water system and nutrients in order to control the qualityFarmer monitoring the hydroponic water system and nutrients in order to control quality. Source: Korawat photo shoot/Shutterstock

Monitoring But Not Too Much

How often should you check and test your reservoir and the liquid gold it contains? Most experts recommend morning or at least daily checks as a minimum standard. Twice daily isn't too often, especially if you've made some changes recently, like starting a new crop, making a shift to blooming or fruiting, or using a new nutrient blend. Equipment upgrades or changes call for closer monitoring, too.

Cleaning & Sanitizing

A clean reservoir signals a well-maintained system. Keep a tight lid on your nutrient tank to control algae growth and reduce the risk of particulate matter like dust, dirt, and leaves entering the system from above. A tight-fitting lid also limits moisture loss through evaporation. Add strainer socks or bags to keep debris from entering the tank through drain pipes.

After a weekly or periodic flushing, wipe down the tank with a safe cleaning solution like hydrogen peroxide (H₂O₂) or bleach, and check the fittings. This is also a good time to clean the filters, scrub the air stones, rinse any dirty strainer bags, and perform other housekeeping tasks.

Read More: Two Methods to a Great Clean - Sanitizing and Sterilizing

Keeping Records

If you've maintained a hydroponic setup for a while, you know the value of good record keeping. Though every project is a little different, if you're paying attention, you'll begin to recognize patterns, especially if you tend to grow the same plant varieties again and again.

Recording your nutrient reservoir test results will help you understand your system better and, over time, make it easier to relate those results to your observations of plant development and behavior. Good records in the form of checklists and detailed notes can be the secret weapon you need to grow prize-worthy plants.

Read Next: Perfecting the pH of Your Hydroponic Nutrient Solution


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Written by Sara Elliott | Gardener, Writer

Profile Picture of Sara Elliott
Sara Elliott is a professional writer with extensive horticultural knowledge acquired through theoretical study and practical experience. You can find her gardening and lifestyle pieces in print and online.

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