Sizing a pump for your hydroponic systems 

How big of a water pump should I get is one of the most asked questions by new hydroponic growers. But the fact is there just isn’t a specific answer that fits for everybody. There are just too many variables in how people can design their hydroponic systems for there to be a clear cut answer that would be able to apply to every situation. The only answer that would apply across the board is get a bigger pump than you think you will need, because you can always reduce the water flow, but you can't do anything to increases its maximum water flow.


However it’s actually much easier than it might seem to figure out what pump size you need than you might think. All you really need to know to do that, is know a few things about the hydroponic system your building first, and a couple things about submersible water pumps. Then you'll be able to tell at a glance if a pump will work for your situation or not.


Flood and Drain systems (Ebb & flow)
First you are going to want to know how much water your going to need to pump. It doesn’t mater what your using for the growing chamber, or how many of them you have, it's the same simple process to calculate the water volume. If the container doesn’t have the gallon size written on it, just fill it up with water to the water level you want, but just make sure to keep track of how many gallons it takes. That gives you the water volume you need to fill/flood it.

If you plan to have multiple growing chambers, just multiply how many growing chambers you  plan to have by the water volume in the one you tested. That will give you the total water volume you need to fill the entire system.

After you know the water volume you need to pump, you will need to figure out how high it will need to pump it above the water line in the reservoir. For that you will need to know where your going to be putting the system and reservoir.  As an example, if your putting the system (growing chamber) on top of a table, and the reservoir on the ground near it, the system will probably be somewhere between 2 and 3 feet above the water line in the reservoir. If your mounting the system along a fence or wall, the height could be much different. Knowing how high the pump will need to pump the water up from the reservoir is a very important aspect of picking a pump (probably even the most important thing to know). 

Once you know those two things about your hydroponic system, then you can go ahead and pick a good pump for your system. For more on picking the right pump, scroll down to the section on “What you should know about water pumps for Hydroponics.”

Drip Systems
While drip systems are simple in nature, there are hundreds of different ways to construct them. But that also means there is almost no end to the variables that could affect the water flow from the water pump. However the same two things you need to know to pick a pump for a flood and drain systems are ultimately the same for all systems (including drip systems), “Water volume and how high you need to pump it.”   

Naturally deciding on how much water (GPH) you want/need to run through your drip system is more difficult to calculate than a flood and drain system. It's not as important because your not flooding a system in a specific time period, your just giving the plants a gentle soaking that can last 15 min, hours, or even 24/7. And you can easily adjust the soaking time with a timer.

Because of things like the size of your plants, how many plants your growing, the type of growing media your using, how much growing medium there is for each plant, how you built your system, if your using a timer to control the watering cycles, as well as how long between the watering cycles, even humidity levels, the amount of water volume you want to reach each plant per hour (GPH) can vary drastically. So there is no easy or set formula to go by for that.  But as mentioned earlier, as long as each plant is getting a steady amount of dripping, you can adjust watering/wetness with a timer.

When considering a water pump for a drip system, water pressure will be the key to it working well. The more plants and dripprs you have, the more water pressure you will need. Submersible pumps used for hydroponics don't give pressure ratings (psi). They only give gallons per hour (GPH) and “head height” (max height it can pump). The the higher the head height, the more water pressure the pump will have. Scroll down to read more about it in the section “What you should know about water pumps for Hydroponics.”

NFT Systems
With a NFT system you don’t need to fill the system (growing chamber), you just need a constant flow 24/7 to all the plants. The water depth is shallow, only a few millimeters (¼ inch or so). So you don’t need a large volume of water to be pumped through it. Typically NFT systems are constructed using long tubes that are angled so the water flows downhill as it flows through the tube. The angle of the tube will control the water depth, as well as the speed in which the water flows through it (not the pump). The pump just needs to be able to keep up with how fast the water is flowing out of the tubes.

With the water depth being just a few milometers, you only need to pump a few gallons per hour through each tube. It doesn’t need to flow fast, but you definitely don't want it to be stagnate. Stagnate water will become depleted of oxygen and nutrients quickly. Flowing water will provide a continues supply of both. 

The water depth and flow rate will be the biggest factors in the gallons per hour you will be pumping. As an example, with a water depth of ¼ inch deep, and 4 inch wide tube, a 10 foot long tube will hold about ½ gallon of water. If you want to recirculate that half gallon of water every 5 minutes,  that would give you 6 gallons per hour through each tube.

If you wanted the flow rate to be faster and changed the angle of the tube so it was recirculating that half gallon of water every 2-½ minutes instead, then you would be pumping twice as much water at 12 gallons per hour. The length of the tube in your NFT system isn’t really important, and wont affect the flow rate or GPH you need to pump. It will only affect the total amount of water needed in your system, but not how fast you recirculate it.

Now that you can figure out the GPH you will need to pump through each tube in your NFT system, just multiply it by the amount of tubes you plan to have in your system to get the total minimum GPH. But always get a pump that can pump more than you need. And don't forget to take into account how high it needs to pump it. For more about pumps, scroll down to the section on “What you should know about water pumps for Hydroponics.”

Aeroponic Systems
There are two types of aeroponic systems. The true aeroponic system uses high pressure (60-90 psi). However most people refer to low pressure spraying systems as aeroponic systems as well.

High pressure aeroponic systems don't really use a water pump due to the numerous cycle (on/off) times needed. They usually consist of  a two sided tank with a rubber divider. The nutrient solution is in one side. And air in the other. Then an air compressor is used to pressurize the tank. A water line from the nutrient solution side runs to the misting heads, and a solenoid  is  used to open and close a valve in the water line at precise times using a cycle timer.

Low pressure aeroponic systems are what most people are referring to when they mention aeroponics. Low pressure systems use standard submersible water pumps, but still need a good amount of water pressure or the water will just trickle out of the sprinkler/mister heads. The more sprinkler heads your using, the more water pressure you will need. Unfortunately submersible pumps don't give a psi rating to compare. They only give you GPH and head height, and GPH is a measure of volume, not pressure. Your best indicator of water pressure is the “head height” rating. It takes pressure to pump water up, so the more GPH it can pump higher, the more water pressure it will have.


The water pumps used for hydroponics are just simply submersible fountain and pond pumps that you can get at most home improvement stores. Some manufactures also package them specifically for sale at hydroponic supply stores. 

Once you know the minimum number of gallons you need to be pumped through your system, it's easy to choose a pump. But we would recommend to make sure you choose a pump that can pump at least twice as much water than the minimum gph of what you need. That will allow you some flexibility in how you set things up, changes in the future, as well as make sure the pump doesn’t fall short of your expectations.

You can always easily reduce the water flow from a pump if you need to, but you cant ever make it pump more than it was designed to. Most pumps will have a flow restrictor built in, it's just a cover that slides/pivots over the opening for the water inlet to reduce the water inlet opening size.

If you need to reduce the water flow even further, the easiest way to do it is just install a “T” connector in the tubing going to your plants, just above the pump and still inside the reservoir (like in the picture on the right). Then install a short piece of tubing on it so half the water goes straight back into the reservoir. If you want to fine tune the water flow even more, you can also add a valve on the end to adjust how much water goes back into the reservoir.


GPH
GPH stands for Gallons Per Hour, and all the pumps will have the maximum gph listed in easy sight on the package. If the pump gives a range like 300-500 gph, it's usually because it has two different size adapters. Using the smaller one will give you the the smaller max gph, and using the larger adapter would give you the higher max gph. But the max gph is only at ground/water level, or one foot high depending on the manufacture. The higher up the pump needs to pump the water, the lower the gph it actually puts out will be. That's called “Head Height.” Some pump manufactures will give a chart or list the max gph at different heights. 

Now make sure to keep in mind that GPH is per hour, not per minute. If you want to know the gallons per minute, just divide the gallons per hour by 60. That's important to keep in mind, especially if you are getting a pump for a flood and drain system. You don't want it to take an hour to finally flood your system, you'll want to be able to flood it in just a few minutes. As an example if you need 50 gallons of water volume to flood the system, and you want it to fully flood within 10 minutes, that’s 1/6th of an hour (50x6=300) . So that would equal 5 gallons per minute, and/or 300 gallons per hour minimum. 

Head Height
The higher the pump needs to pump the water up (vertically not the amount of tubing it is pumping through), the more back pressure there is on the pump from the weight of the water and  gravity. The point when there is more back pressure on the pump than the pump can put out is the “ Max Head Height.” At the water line there is no back pressure on the pump, and that's when you will have the maximum water flowing that the pump can provide. If it needs to pump 3 feet high before it gets to where it's going, there will be 3 feet of back pressure that the pump needs to overcome before any water can flow out. 

 When choosing a pump, it's important to keep in mind how high up from the water line in the reservoir it will be pumping up to. After all, because of head height the actual gph it can pump to that height can be much different than the max gph on the front of the package. Most manufactures give you some kind of chart showing the max gph at different heights to judge by.

Always look for the pump that has the highest head height for the price range. While submittable pumps don't give you a psi (pressure) rating, it takes pressure to overcome the back pressure. So the pumps with the highest head height and thus can overcome the most back pressure, will naturally have the highest psi as well.

Cleaning the Pump and Filters
Submersible pond and fountain pumps are just electromagnets. The coil is in the main body, and the impeller shaft has a magnet. Water can get in-between the impeller shaft and main body, and it acts like a lubricant. There are just a few basic parts, the main body, the impeller and shaft, the flow restrictor, impeller cover, and inlet opening cover. It can be taken all apart and cleaned. You should get used cleaning the pump with every nutrient solution change. It's easy to do especially when you do it regularly. Just take it apart and use regular dish soap and a sponge or brush.

The pump you get may or may not come with a filter/screen. But don't worry because even if it doesn’t, you can easily make one cheap from common things. First you want to take the water inlet cover off. For about two or three bucks you can get a furnaces filter screen from any hardware store, and some places like walmart like the one in the picture on the right.

Just cut out the white screening out to use as your filter screen. Then just cut a piece to fit snuggle inside the water inlet cover. Then just place the cover back on. You can also use the blue swamp cooler pads as well, or even a cheep sponge as long as it doesn’t have a side for scrubbing, just the foam side. As for cleaning the filter all you need to do is put a dab of soap on it and work it in under running water, then rinse it out thoroughly.