Tropical fish - How many hours a day does the air pump need to be on?

What exactly do you mean by air pump, what size tank is it, what fish are you keeping and what are the water chemistry readings exactly?

If you mean something that blows bubbles into the water, and that's it, such as through an air stone. This is ornamental, the action of the bubbles popping on the water will help with oxygenation in the water, but this can be achieved more easily by putting the filter outlet blowing across the surface of the water. Its the surface movement that puts oxygen into the water.

If by air pump you mean the filter (with filter sponges etc) then this needs to be on 24/7, only off when you're doing your weekly partial water change. When its off the beneficial bacteria in the filter media will start to die, and ultimately destroy your water quality and kill your fish.

Air pumps and aeration

Air pumps can be used in two main ways in the aquarium: either to power small internal filters and undergravel filters (UGF) or for aeration only, using airstones. When used to run UGF (by placing the airline in the uplift tube), an airstone should be attached to increase the number of bubbles and hence water movement.

It is not really the air bubbles themselves which aerate the water per se, it is the circulation and surface turbulence that they create. Good circulation in an aquarium can be important for several reasons, but one of them is to circulate the water up to the surface where it will interact with the air to pick up oxygen - this is why surface turbulence increases the aeration/oxygenation of the water.

Picture of air-powered filters

Note that in an aquarium with good circulation, additional aeration should not normally be necessary. In planted aquaria it is actually undesirable, as it will cause more of the CO2 on which plants rely to be lost from the water. There are occasions where it may be desirable to increase oxygenation however. One of these is when the temperature of the aquarium is higher than normal, due to high ambient temperature. There will be less oxygen dissolved in the water as the temperature increases, so it is important to maximise aeration in a warmer tank.

Airpumps come in a range of sizes to suit different size aquariums and accessories. Some are provided with twin outlets, while others have adjustable flow. Control valves, T-pieces, etc. can be used to divide the flow to several Aeration devices.

An airpump should normally be placed above the level of the aquarium, so that in the event of a power failure, water will not drain back into the pump and damage it. If the airpump is placed below the aquarium, a non-return valve should be fitted into the tubing line, which will tend to reduce flow slightly.

Note that you should not restrict the flow from an air pump, as this is likely to damage it. If you are using a larger airpump to run just one airstone for example, you should use a double valve so that the 'excess' air can be bled to the room.

Air pump, on all of the time.

If you think it's waste, then kit out your tank with an under gravel filter system (regardless of whether you have a filter or not) that way the air line is doing more functions maybe making it a bit more worth while, for you.

try not turning off the air pump, cuz that supplies a lot of oxygen to them.

see what happens in terms of fatalities after not turning off the air pump at all for a week or two.

good luck :)

usually tanks dont need them unless there are loads of fish in ect. i have one in mine, but its mostly used for effect i dont think the fish need it. and if you mean a filter then it should be left on 24-7

idiot! you have to keep the pump on at all times day and night! you just killed the fish! the pump supplies oxygen to the water