A powerhead is a device that looks like a little internal filter but has no filter material in it! Its simply a pump that takes in and spews out water in the tank itself! So why keep an equipment that just moves water around?
A powerhead is actually quite useful in some tanks; in others, it is almost essential.
A powerhead will create a underwater current, keeping the water moving around your tank and causing your heaters to actually heat all the water. Not only that, the current will give your fish something to swim against, which is appreciated by active river fish that otherwise will spend their lives wondering how they ended up in a small glass pond.
Of course, some fish don’t like a great deal of current, but most fish robust enough to live in a large tank environment appreciate some current to frolic and play in. More importantly, the flow of water means that your water maintains a homogeneous temperature throughout the tank without developing unhealthy cold and hot spots that will confuse the fish and potentially make them ill.
Powerheads provide important water circulation and oxygenation in the aquarium, far more efficiently then the bubbles from air stones do. The more your tank water is circulated and filtered, the better the water quality is in the aquarium. They help to keep detritus and other tank matter from settling on the bottom of the tank. Powerhead circulation permits the majority of these particulates to be circulated or suspended, allowing them to be filtered out by a mechanical filter.
Pick a powerhead that can be taken apart and put back together easily. Unwanted matter at times can enter the impeller area and needs to be removed. Look for ease of cleaning to prevent restricted water flow, which in turn can lead to the unit burning out prematurely from overheating.
Its nicer if the powerhead has a strainer or screen of some type that covers the water intake hole to prevent unwary tank inhabitants from getting sucked into it. Check the size grid of the holes on the strainer and choose the larger sized one. Ones that are too small can slow the water intake.
Flow Rate: You want to aim at turning over the tank water at least 6-10 times per hour. Many aquarists feel that you cannot have too much water movement, and nowadays, striving for a 15-20 times per hour ratio is not unheard of. We feel this is not necessary for a fish-only tank, but is beneficial for a reef tank. You want to give the tank sufficient water movement and circulation, but not so much that the fish can’t move against the currents, or the other tank inhabitants are getting battered by it.