There are a lot of pumps out there on the market for the home aquarium. So many, in fact, it can be a daunting task to make a decision on which one is best for you. There are air pumps, circulation pumps, system pumps, and an endless amount of other fancy names given to a group of pumps to increase their marketability. Of these, "system pumps" are the most crucial. These are the pumps that you use as the main water movement mechanism between your tank and your filter. Now, there are a lot of filter setups that can be purchased for your home aquaria. The manufacturers suggestion should be followed with regard to any system where the water is maintained at or above the base of the tank. In other cases, the water maybe required to flow below to a sump or refugium that may reside underneath the main system. In this case, manufacturers generally do not give any recommendation as to what size pump you should use. Some may suggest a BRAND, but they do not know your particular setup and are unable to give much more information than that. In most of those cases, they have worked out what is called "co-branding" with the pump manufacturer to suggest each others products. Your local fish store may suggest a particular pump as well. If you are not educated in what your needs REALLY are, you may not get the best pump for the job. Most fish stores will treat you right, it is in their best interest to do so. But, there have been some that push one BRAND more than another, because they get a higher percentage profit from it. This is hardly the case, but you still need to know what your system actually requires to ensure you are getting what you need.
There are a lot of brands on the market. Aqua Medic, Danner, Dolphin, Eheim, Iwaki, TAAM, Two Little Fishes and Zoo Med to name a few. This article is not going to compare one particular manufacturer to another, that will be in the reviews section on FishDB. Here we are just going to educate you on how to select the right pump for the job. You will inevitably here someone say, "it is more expensive, but it is a better pump." That may very well be true, but is it the right pump for your system? To answer this question, there are really only two things you need to know. First, how many gallons per hour do I need it to move? Second, what head pressure will this pump be fighting against?
What is your target flow rate?
Typically, pumps are rated in gallons per hour (GPH), gallons per minute (GPM), liter per minute (LPM), pounds per square inch (PSI), revolutions per minute (RMP), horse power (HP), and amps (AMP). Flow rate is GPH, GPM, or LPM. If you require metric figures, you can use the LPM instead of GPM and multiply it by 60 to get LPH (liters per hour). But, in our example we will use either GPH or GPM. The other measurements have their place but we do not need them in this particular case. So, now we know what those letters mean, what exactly do you need? The general rule of thumb in regards to cycling the system water through the filter media is 2 to 3 times and hour for fresh water tanks, 3 to 4 times an hour for salt water fish-only tanks, and 8-10 times and hour for salt water reef tanks. For example, if you have a 75 gallon reef tank, you would want that amount of water to pass through the filter about 9 times in one hour. This means that your desired flow rate should be 675 GPH or 11 to 12 GPM. (75 X 9 = 675 GPH and 675 / 60 = 11.25 GPM) Depending on you actual system layout, this may or may not be enough to cause adequate water current inside your tank for corals and sessile invertebrates without the need for supplemental power heads. If the world were flat, that would be all you needed to know, but it isn't.
What is your head pressure?
This is not the pain you are feeling in your temple or behind you eyes right now. Head pressure is the vertical distance a pump must push against. Every pump out there, loses efficiency when it has to push water upwards. Some more than others. Most manufacturers have started providing a graph with their pump specifications to reflect their pump performance. Here is an example of one of those graphs. Head pressure is very important when selecting your pump. Even if you only have to push up 3 feet, some pumps could drop from a 750 gallon per hour (GPH) pump to about 350 GPH. Others may not be effected noticeably until a greater head pressure is introduced. So before you buy a pump, figure out exactly how many feet (meters) it is from the outlet of the pump to the highest point it has to push. Notice I said the highest point and not the hose outlet. If the outlet of the hose is laying on the ground next to the pump but the hose goes up and over an 8 foot wall, then the head pressure is 8 feet. It still has to push the water up the 8 feet before it can reach the other end. Not all water pumps you look at will have head pressure ratings. This is not to say that the pump will not work for you, but buying a certain GPH pump without knowing the manufacturers head pressure ratings may leave you with a pump that does not do what you expect. Now you are armed with two things. You know your desired flow rate and you know what your head pressure is . So which pump to buy?
Selecting your pump
Now you can take what you have learned and pick the right pump for the job. This does not take into effect, which pump will last longer than others, but rather only pump ratings and specifications. Nowadays, pump manufacturers print head pressure graphs on their boxes or make them available on the Internet. In this photo, I have zoomed in on the area that is of interest to us. This is the performance chart for Iwaki brand pumps (used as example only). Previously we were using a 75 gallon reef tank with a 8 foot head pressure as our example. From that we determined that we needed about a 11.25 GPM flow rate. In this graph, the numbers on the left are head pressure heights and the number across the bottom are flow rates. If we find the 8 foot mark on the left side and the 11.25 GPM flow rate across the bottom this will be your starting points. Now move right from the head pressure number and up from the flow rate till they intersect and you should meet at the blue dot I created. Once that intersection is found, we are able to see if any of this manufacturer's pumps meets out criteria. In this example, Iwaki Pump model number 30RXT does just that. This pump should preform well for our needs. Again, this article is not intended to prevent you from obtaining advice from your local fish store, but rather, to give you the tools needed to answer their questions when they ask you.