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How Big of a Reservoir Do Hydroponics Need?

When any grower begins looking at building a hydroponic system, one of the main components will be the reservoir. Because the entire process revolves around water, this will need a home that is worthy of the life giving essence that the water provides.

The question arises for many growers because they may be trying to figure out what will fit where in their designated growing area. “How big of a reservoir do hydroponics need?” There is a general rule for this, which we will see, yet there is much more to determining the size of a nutrient reservoir than just having one of a specific size.

Carry on reading for all you need to know about hydroponics tanks and how you can be sure you have one that will meet all the needs of your system.

Do You Need Hydroponic Reservoirs?

Reservoirs are a fundamental component of any system. If it weren’t for these, there would be no place to put the water and nutrient solution. There are a few aspects to go through rather than just thinking a reservoir of a certain size is good for a given number of plants.

One of the first to know is that the size can change depending on the type of system you are looking to run. However, no matter what system you are using, the consensus is that the bigger the reservoir, the better it is for your system.

The reasons for this are a larger tank can help with pH swings, nutrient solution fluctuations and the depletion of oxygen. As soon as any of these factors are affected, then there is a knock on effect with the rest of the system and the plants.

You can add to this how the environment plays a role in the operation of a reservoir. Plants will change their uptake of water and nutrients depending on the environment, and if the humidity is lower than the ideal 60 and 80 percent, and is lower than forty to fifty percent humidity will cause plants to take up much more water to compensate.

If it were just a basic calculation to determine the reservoir size, this would be easy. As a rule, there should be the following:

  • Small plants: 1/2 gallon of water per plant
  • Medium sized plants: 1 – 1/12 gallons of water per plant
  • Large plants: 2 1/2 gallons of water as a bare minimum

Although these are the recommendations, many seasoned growers will double these volumes without a second thought just to be sure.

How Do Systems Use Reservoirs?

Here is a quick look at the different systems and how a reservoir fits in with their design.

  • DWC (Deep Water Culture): Plants are suspended over the top of the reservoir. The solution will be highly oxygenated as no water pump is used.
  • Ebb and Flow: The reservoir sits under the flood table. Using a timer, this is flooded periodically. Once the timer cuts off, then the solution drains back to the reservoir.
  • Drip Systems: Reservoirs sit lower than the plants. A pump will feed solution through small tubes where it drains through the growing media and makes its way back to the reservoir using gravity.
  • NFT (Nutrient Film Technique): A thin stream of water is continually pumped into the highest point of troughs or channels. Plants are suspended over this so their roots can hang into the solution. Gravity is the usual means of returning the solution back into the reservoir.
  • Wick Systems: A thick rope will sit in a reservoir and feed up to the growing medium in a container sitting on the top. Plants will be fed by this wicking action, which delivers nutrients upward.

The Roles of Hydroponic Reservoirs

Here are the areas where reservoirs help to keep systems running at their best. As we have just seen, each system can use their own reservoir in a different way. However, all the following will be common, regardless of the system, the plant type or the location.

These few areas are what makes your system tick and stay healthy.

Nutrient Preparation

Your reservoir is the ideal place where to mix your nutrients. Some growers may mix in a separate container and then add to the reservoir, yet this makes little sense to add more work into the equation.

In an ideal world, you should have a spare reservoir, and this is where you will be mixing your next batch while one is in use.

Water Oxygenation

Without oxygen, plants die and will die quick. Depending on the system type, these solutions need lots of oxygenation through the use of an air pump. This then has tubes running into the mixture, and air stones or air diffusers convert this into tiny bubbles, which the water absorbs.

While some of the systems use the water cascading back into the reservoir, this doesn’t deliver as much oxygen as a good air pump.

Concentration of Nutrients

As water is taken up by your plants or water levels drop by environmental factors. This means the concentrations of the nutrients increases. This will be very different from when you first mixed the batch, and will make it harder for plants to absorb what they need in the right amounts.

Your solution will need continual testing and adjustment as is required. Yet, the larger your reservoir, the rate at which the solution changes concentration is somewhat diminished. This can help reduce the amount of testing, and space out the intervals for replacing solution.

A good EC (Electrical Conductivity) meter can take a quick reading and let you know the levels of nutrient concentration. There is no way at present to determine what levels of each nutrient there is in the solution.

Ease of monitoring and adjusting solution pH levels

Just like EC levels, the pH of your solution will fluctuate. This can be from a change in concentration or there is a change in the temperature. Holding a pH in the desired ranges is vital for the health of the plants.

When you have a change in pH, this can lead to nutrient lockout or nutrient toxicity if it swings the other way. The larger the reservoir, the slower the rate of change of your pH. This makes testing more straightforward and not required as often. You can find adjusting pH is easier when there is a larger amount of liquid.

Solution Temperatures

A small reservoir can heat up much faster than a larger volume of water. Plants like temperatures between 68 and 75 degrees fahrenheit for their solution. It doesn’t matter if you live in colder areas or warmer, this larger volume of water is easier to control once you heat or cool it.

One sure way to help with maintaining solution temperatures is to use insulated reservoirs. These will help even more in keeping the temperatures stable without the use of a hydroponic water chiller or heater.

Reservoir Considerations When Choosing

Before purchasing any reservoir, there are some things to consider aside from the above. While all tanks may appear appropriate, this isn’t the case.

In this section, we will look at all the factors, which can determine your final choice of reservoir for your hydroponic system.

Reservoir Construction

Many gardeners construct their own systems. This leaves the choice of materials for their reservoir very different from if they were purchasing one. While it leads for lots of creativity, this is often done more for cost saving.

Large plastic totes can hold massive amounts of water, and thus can be a viable solution. However, once these are filled, it can lead to issues, which are not noticeable in the beginning.

Once these containers get warm over time, they begin to deform and bulge outward. There are many reservoirs, which are made from durable and sturdy materials that are a better choice. Barrels or large picnic coolers can be great options, and in most cases, they will be made from food grade materials such as polyethylene.

Reservoirs Need Lids

Depending if you construct your own reservoir, or purchase one specifically will determine if it comes with a lid. While these don’t appear to be too important, they are in fact crucial for a couple of reasons.

A lid on your tank can reduce the evaporation of your solution, this helps maintain the EC and pH levels to what they should be.

Reservoir Color

Aside from a lid preventing evaporation, there is the fact that as light begins hitting your solution, there will be algae growth. Algae can deliver a whole host of issues like depleted nutrients and oxygen from the water.

The time between cleaning this growth from your tank can also reduce. While dark colors are a recommendation to prevent light seepage, these can absorb heat from grow lights. Covering tanks in silver foil or insulation can help keep light out and keep your solution cool. It is worth noting that warmer solutions can’t hold dissolved oxygen as well as colder solutions

Tank Location

This can depend on the kind of system you are running, but not only that, once they are full of water, there is no way you can relocate them.

Your reservoir will need to be out of any direct sunlight and it should ideally be close to a water source and a drain. This can make topping off and cleaning that much easier. One other thing that may have a bearing on this is the system type.

Many tanks sit under the bed of the system. Accessing the tank while the garden is in use can be very difficult. There will be hoses, pumps and pipes all over the place, which can be hard to dismantle to gain access. There is also then the consideration of how close the tank is to the grow lights. Hence the dark color and the silver insulation.

Care and Cleaning of Nutrients and Reservoirs

A reservoir and the solution it contains will only be as good as the care and attention it receives. It isn’t possible to fill one and then expect everything to be fine until it is almost empty. Here are some things to know about the care and attention for both elements.


There are many methods of testing solutions to be sure the levels are correct. While you can use manual means of doing so, these are not as effective as meters, which can make these readings in a much shorter time.

There are expensive automated means of doing the same thing, yet meters are not worth anything if they are not used. It is possible to purchase multi-purpose meters that are capable of taking readings of different elements like pH, EC and the PPM/TDS.

Many gardeners now use this kind because of the timesavings when testing. Not only this, but they are more accurate that manual testing means. One thing to be sure of is that any device you purchase can have manual calibration. This can prolong their accuracy and their life while reducing errors.


We have seen how vital dissolved oxygen is for plant health. The best ways to do this are through air pumps and air stones. The benefits are still being seen, so it is better to have more oxygen in your water than too little.

The other plus side of this is it prevents water stagnation and keeps nutrients being continually mixed and stimulated. This aeration can actually help with the nutrient uptake by your plants, and thus helping promote plant growth.

One area, which may not be seen by new growers, is that this aeration can help prevent any development of pathogens. Rather than any anaerobic bacteria forming, there is the growth of many other organisms that are beneficial.

Topping off Tips

Every grower has to top off his or her tank at some stage. Up until this stage, there will be lots of testing and waiting. However, levels will begin to drop the longer the system is running. We saw that nutrients strength increases because water take up is higher than nutrients.

This means that water needs adding to make sure plants have enough, and to dilute the nutrients before they become toxic. However, there is only so many times you can top off a hydroponic reservoir before the nutrient solution becomes too weak, and you are in need of mixing a new batch.

When first filling, you need to mark the high water level on the inside of your reservoir. This will need checking daily, and you can top off up to that level as required. This happens every few days rather than daily.

While doing this you will need to keep a check of how many gallons, you add. A good rule to follow is that once you have replaced 50% of the original volume, then this is time to consider flushing the system.

Reservoir Flushing

It doesn’t matter how large and how good this larger volume of solution is at buffering changes in the nutrient levels or the pH. There comes a time when you top off the the extent that the solution is weak, there is debris in it, or you are having issues with nutrient deficiencies you just can’t work out.

Having a clean tank is the ideal way to solve most problems, and it is the only time you know what your levels are. There are long conversations and debated when the best time for system flushing is, yet you can find that even if there is no real right time, there is definitely no wrong time.

It can be as little as a few days before your levels start changing from the ones you set, so it is easy to see why this system flushing occurs on a regular basis. Some gardeners may flush weekly, while others recommend bi-weekly. This is true for vegetables, which can take on a bitter taste through too much nutrient absorption.

Hobby gardeners can follow this and flush more often than not. This can resolve issues from beginning without affecting their plants.


As we can see, there is no real upper limit on size of hydroponic reservoir, yet being realistic does come into it. The main thing to consider is that you don’t choose one, which is just the right size or smaller. This can leave with continual issues you need to deal with, and you have no way to turn to offer a solution.

You can see why gardeners come up with the recommended size by the number of plants and the volume of water for each plant before doubling it. These buffers can make all the difference between healthy crops and a failed crop.

With the reservoir, that is the ideal size, and if possible, a second where to mix and use as the other is out of commission can lead to less downtime and a healthy yield from your garden. For the gardeners who can’t afford or fit in a second tank. All the above information should be enough to make sure their primary tank is large enough and cared for to give a healthy system.