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INTRODUCTION

Aquarium circulation means water movement. It is very important part of successful aquarium keeping and often misunderstood by hobbyists. Many devices create water movement - aquarium water pump, aquarium powerhead, fish filter, wavemakers or even aquarium air pumps. What do you actually need for your tanks? How to combine devices that fulfil those needs?

This article guides you :

To understand aquarium water flow importance
Measuring water movement needs for different types of aquariums
Reviewing the devices that create the water movement and finally choose the right ones for your tank

Read all about Aquarium Circulation by clicking the next tabs.

AQUARIUM CIRCULATION IMPORTANCE

Gas Exchange

Gas exchange means bringing in oxygen and escaping waste gases, surface agitation makes the process run well. In still waters with low water movement like lakes or ponds, gas exchange occurs through the water plants - aquatic plants consume CO2 for photosynthesis and release oxygen during the daytime, and use oxygen for respiration and release CO2 at night. So the water surface movement is not the primary media for gas exchange in natural still waters.

Many debates in aquascape's community regarding water agitation issue. Aquarium plants need CO2 that can easily escape if vigorous water agitation applied, so minimal circulation and surface water movement is needed to keep the CO2 inside. But poor surface agitation cause difficulties in oxygen dissolving process and escaping other waste gases like Nitrogen. Besides, classical surface problems in planted aquarium will occur if you apply minimal surface agitation.

How to solve this problem ? Please read our Aquascape supplies article to find inspiring solutions.

Diffusing Oxygen and Nutrients

If your aquarium is heavily stocked, dissolved oxygen from water agitation is not enough to sustain livestock and the bacteria that process their waste. You need to add aquarium air pumps for supplying oxygen into your tank.

Surface movement can't distribute oxygen evenly throughout your tank, you'll need additional aquarium water pump to create adequate circulation throughout your tank. Inadequate aquarium circulation will form anaerobic spots in places where lack of oxygen supplies. It's dangerous, because the anaerobic bacteria that live there usually produce toxins or harmful chemicals. Besides, adequate aquarium circulation is needed to evenly diffuse the nutrients that needed by aquarium plants.

Making aquarium filtration works

Fish tank filters receive inputs from the water around their input-units. If there's no water flow to bring waste to them, they can't do much to clean and detoxify your tank. Waste will precipitate in your aquarium bottom, so you need additional fish tank pump to create flows that bring waste to the filters.

Filter and water circulation at once can only be applied in small tank where its limited space is too small for additional fish tank pump.

Water Conditions leveling

Your aquatic friends like fish, shrimp and crayfish can only adapt with slight changes in water conditions. Major changes in water parameters can shock your organisms and finally kill them. Good aquarium circulation is very important to stabilize water conditions - especially oxygen, temperature and salinity - in the entire aquarium. Please note that aquarium heaters and chillers affect only one area within your tank, water flows will mixed the aquarium water, creating same temperatures, same dissolved salts and oxygen throughout the aquarium. It's important to have right water parameters readings to take necessary actions.

Slow algae-growth down

Algae can grow everywhere in your aquariums, not only at aquarium glasses, it can form algae slick on your water's surface, stick to aquarium plants or even free-floating within your aquarium water creating green water. It's true that algae is not avoidable at any aquariums, but you can slow down their growth with proper aquarium circulation and agitation.

I think adequate water movement absolutely needed for all aquariums, including planted tank. Aquarium water pump will create water flows that prevent algae to form slicks on the surface and make it difficult to stick at any surface.

CALCULATING GPH PUMP

Don't just buy any aquarium pumps for your aquarium circulation !. First, you need to calculate the capacity of your aquarium water pump (gph pump) to get proper circulation. It is simple, just multiply your tank volume with the turnover rate to get the gph pump. Turnover rates are the estimated hourly water-turnover needed for your specific tanks, it vary and mostly depend on the organisms that you keep.

Tank Type	Turnover Rate
Freshwater Fish-Only tank	4 times per hour
Planted Tank	2 times per hour
Tanks with Small Freshwater Fishes (like tetras, bettas) or fry tanks	2 times per hour
Tanks with Large Freshwater Fishes (like piranhas, oscars) or Turtle Tanks	5-6 times per hour
Saltwater Fish-Only tank	5-10+ times per hour
Saltwater Reef	10-20+ times per hour

For example, if you have 50 gallons tank and turnover rate is 4 times in an hour, you'll need a gph pump at 200 GPH (50 x 4).

It's necessary to get higher gph pump by adjusting the turnover rate by 1 or looking for the next highest GPH rating - especially if you use filters for circulation devices where accumulate waste in filter media will slow down the water flow.

REVIEW OF CIRCULATION DEVICES

Please note that you shouldn't use filters as your primary circulation except in small aquariums (below 50 gallons) where water flows from filtration are enough for their limited spaces. Different types of filters have different flow rates. Check their gph pump ratings, match with your aquarium circulation needs.

In time, your filters will slowly loose the flow due to waste accumulation in the filter media. That's why you should more concern about regular maintenance to your filters, regular cleaning your filter media like bio-balls and bio-rings and replacing your filter-mat can keep the flow rates.

Aquarium Circulation Devices	Descriptions	Recommendation
Aquarium Air pumps + airstones	Aquarium air pumps are not designed for aquarium circulation, although in small aquariums it can create sufficient water movement. They are good for supplying oxygen to your tank and creating surface agitation to aid in gas exchange. You can change your airstones with sponge filters to get more benefit of mechanical and biological filtrations.	Anyway, aquarium air pumps are needed in all aquarium sizes due to their primary functions.
Sponge filters Undergravel filters Box or corner filters	These filters use aquarium air pumps to power them, creating slow water movements.	Only suitable as primary circulation in small tanks, quarantine tanks and fry tanks.
External (HOB) power filters	Produce waterfall flows, check the filter size to get suitable gph-pump ratings for your tank.	Only suitable as primary circulation in small tanks.
Internal power filters	Creates middle-level flows, poor water agitation to break water's surface tension.	Only suitable as primary circulation in small tanks.
Aquarium Canister filter & Wet Dry filter	Aquarium canister filter is surely pressurized filter while wet dry filter can be divided into 2 types : canister-type and sump-type. The Canister-type is pressurized wet dry filter while sump-type uses external reservoir of water plumbed into your tank, it needs experience and good plumbing job to make it works. All of them need aquarium pumps, either they come with their own or you have to provide it.	Choose filters that have gph pump ratings higher than you need to counteract any flow loss due to resistance in filter media.
Aquarium pumps	They are special devices for aquarium circulation, they can circulate water evenly with gentle currents. Understand Head Height Head height is the distance from the aquarium water pump to the output unit. GPH-pump rating decreasing as head height increases. So, it's important to plan your aquarium water pump placement to get head height estimation, then you can choose the gph-pump ratings based on that. Usually aquarium water pump will provide list of head height/GPH correlations, for example 150 GPH at 0 head height/100 GPH at 3 feet, and so on. Anticipate Resistance & Plumbing You should anticipate any resistance from your devices that can slow down your water flows especially if you'll use pressurized filters like canister filters or extra plumbing for sump-type filtration. Just increase your turnover rate by 50% to get higher gph-pump rating. I often see some hobbyists wrap their aquarium pumps' input-tubes with plastic sheet to slow down the output flow. You should never do that, it will only shorten your aquarium water pump life. To adjust the output flows, choose fish tank pump with output adjustments valve or attach one for your existing aquarium pumps. Submerged vs External pumps For common use, submerged aquarium pumps are the best choice, they are quiet and very easy to install. They produce some heat, but usually won't affect much to your aquarium temperature. Take up space in your tank is the only disadvantage of the submerged aquarium pumps. External aquarium pumps are more suitable for sump-type filtration that operates at high head heights. Usually, they have 2 configuration options : for high pressure usage and free flow. High pressure setups are needed for sump-type filtration with extreme head heights, extensive plumbing or to supply big pressurized filter in order to get enough gph-pump ratings. While free-flow setups are used for common circulation.	It's necessary to always keep extra aquarium pumps in your storage, you can immediately replace the malfunction pump and fix it whenever you have time. This way is better than to operate more than one fish tank pump (as a spare) in your tank since this device take up space.
Aquarium Powerheads	Aquarium powerhead is small submersible aquarium water pump that usually attach to the aquarium walls using suctions. Some brands provide many attachments like venturi -for aeration-, rotating returns device or wavemakers attachment tube. Aquarium powerhead doesn't take up spaces, so you can put 2 or more aquarium powerhead at different points to create river-like currents. Remember to adjust the flows at comfortable level for your aquatic organisms.	Surface agitation is needed to prevent surface problems like oil slicks or surface scum. You can use split output unit at your aquarium powerhead to create both circulation and surface agitation (use L extension to direct the water flow upwards). But surface agitation using this device only covers certain surface area, to agitate the whole surface you'll need Wavemakers that can be attached to your aquarium powerhead or stand alone. Surface agitation is really needed in heavy-stocked aquariums and turtle tanks.
Circulation Pumps	Circulation Pumps provide continuous and powerful water flow which can be directed freely. Circulation Pumps create high water volume output with low pressure making the pumps energy efficient with low heat emission. They usually include magnet-suction cup mounting system for free positioning in aquarium, easy removal and secure installation.	To simulate natural river and reef currents, they are designed for use with timers and wavemaker systems. They are suitable for freshwater and marine aquariums.
Wavemakers	Wavemakers are specifically designed to replicate the natural alternating rhythms of tides and currents for home aquariums. These wavemakers instantly create turbulent flow patterns with adjustable alternating cycle times. Benefits of installing Wavemaker : • Aquarium transform into a cleaner, healthier and more natural environment. • Provides oxygen rich water to entire aquarium • Provides more stable water temperature • Creates desirable turbulant flow patterns only found in nature • Flushes "dead spots" of detritus and accumulated waste • Increase fish activity	Some Wavemakers options : • Complete wavemaker system packages are Wave timer /control unit + Circulation pumps or Powerheads. ° The system can produce a Wave or Tide Effect by setting the timer (for duration of cycles), using on/off Mode or setting the power of the pumps by operation on the minimum and maximum controls to better suit the needs of the aquarium and its inhabitants. ° Food Mode is used to allow feeding of fish or invertebrates in reef aquariums. ° Automatic Night Mode can slow down the pumps during the night and turned back to the set speed during the day. • Oscillating current wavemaker. This device oscillates the return from your existing pump or canister filter 90 degrees every 60 secs. It operates with any pressure input. It sits on top frame of tank with built in bracket to fit all aquariums. • SCWD wavemaker . The SCWD (pronounced "squid") is a revolutionary device designed to provide alternating currents without the use of electricty. The SCWD will run on any pump with a minimum output of 50 GPH and a maximum output of 1400. The switching speed and current duration is dependent on the volume of water flowing through the SCWD. You can control the duration by controlling the flow going through the SCWD.

CHOOSING DEVICES

After a lot of reading, it's time to choose your aquarium circulation devices. Don't be afraid to experiment with different setups, it will lead you to a better understanding in aquarium circulation. Some tips :

Remember that the first rule of choosing fish supplies is : Buy products from trusted and reputable brand, it will save you from headache later.
Estimate your gph-pump rating up, to anticipate resistance especially if you choose filter as your primary circulation.
Use ball valve to adjust your water flow down, don't reduce the input by blocking or wrapping the input-tubing with something.
If you choose aquarium water pump for your device, keep one as a spare. It's big size make an eyesore if you operate more than one. You can also use several aquarium powerheads to replace one big aquarium pump, combinations between 2 smaller aquarium pumps or one smaller aquarium pump + aquarium powerheads
Aquarium air pumps are needed in all aquarium sizes due to their primary functions : supplying oxygen to your tank and creating surface agitation to aid in gas exchange.
Adjust the water flows until you get the comfortable one for all your organisms, too strong flows can stress your fishes and make them tired. For goldfishes, too strong current can damage the fin and body shape.
Clean your fish tank pump and filter parts like filter media, tubing and others regularly, also replace your filter-mat if needed to prevent resistence that can slow down the water flow.

Finally, you are ready to choose your aquarium circulation devices. Proper aquarium circulation, along with aquarium filtration and lighting are the foundations of successful aquarium keeping.