How to Increase Oxygen in a Fish Tank, With or Without an Air Pump

Check the water temperature

Aqueon says “most tropical fish prefer 74° to 80° F”, and that a fish “needs more oxygen” as the water warms, while “the ability of water to hold dissolved oxygen drops with rising temperature”. Our guide to what temperature a fish tank should be gives each source’s ranges.

Unplug before your hands go in the water

Fluval’s AquaClear filter manual: “Always unplug or disconnect all appliances in the aquarium from electricity supply before placing hands in water, before putting on or taking off parts and while the equipment is being installed, maintained or handled.” For the heater, follow its manual.

If it runs warm, cool it slowly

Aqueon: “Open the aquarium cover and position a fan to blow across the surface of the water. (You may want to lower the water level an inch or two to prevent fish from jumping out.)” For ice (unplug first, step 2), it says to “Float a bag of ice or cold water in the fish tank to gently lower the water temperature. (Take care not to lower the temperature more than 2 or 3 degrees F in a 4-hour period.) Avoid putting ice cubes directly into your aquarium unless you make them with reverse osmosis or dechlorinated water.” Aqueon adds: “always remember to make any fish temperature changes in your aquarium gradual.”

Cut waste and crowding, and change some water

Unplug first (step 2). The Spruce Pets says: “Overcrowding is the number one reason for low oxygen in an aquarium.” It adds: “Accumulated fish waste and algae overgrowth can sap oxygen from an aquarium as bacteria work to break down the excess organic matter.” For routine changes, Aqueon says: “Change 10% of your aquarium water every week or 25% every two weeks.” For gasping fish, The Spruce Pets says to “Perform a large water change (as much as 50 percent of the tank’s volume)”; Aqueon’s general rule differs: “Avoid water changes of more than 25% as larger water changes can stress your fish and upset the balance in your aquarium.” Aqueon’s routine rules: “Replacement water should be the same temperature as the aquarium water.” and “Always treat tap water with a water conditioner to neutralize chlorine and ammonia before adding it to the aquarium.”

Check how the filter returns water

Unplug first (step 2). Complete Koi, a UK aquarium and pond retailer: “If your internal filter or canister filter return pipes are fully submerged, causing little to no surface agitation, it’s crucial to add an air pump.” The Spruce Pets: “A clogged filter must be cleaned or replaced. In addition, you can install a spray bar on the outlet of the filter or add air stones to the tank.” Fluval’s AquaClear manual: “Always unplug power filter prior to cleaning.” Its 07 canister manual: “Rinse biological media with aquarium water, never tap water, or replace as required.” and “Never replace all biological media at one time, as valuable colonies of beneficial bacteria would be lost.”

Add an air pump with an air stone or sponge filter

Unplug first (step 2). Aqueon: “While an air pump is not a necessity, aeration does help maintain the dissolved oxygen level in your aquarium and also aids in biological filtration.” It adds: “Keep air diffusers and bubble wands away from filter intake tubes, as they may cause the filter to stop if air is drawn in.” Our air pump, air stone and sponge filter roundups compare the gear.

Fit a check valve, and set the pump above the water

Tetra’s manual for its Whisper 10-100 pumps: “To prevent possible electrical shock resulting from water back-siphoning, pump should be used with a check-valve or positioned higher than the water level.” Its setup steps put the pump “on a shelf at least 12” higher than the water level of the aquarium, but not directly above the aquarium”, add “(Note: the shelf should have a raised edge to prevent the pump from sliding off.)” and say: “Use a check-valve between the pump and the aquarium.” Aqueon goes further: “A check valve should always be installed to prevent backflow when the air pump is unplugged or in the event of a power outage.” Aquarium Co-Op: “If the air pump is positioned higher than the top of the aquarium, you can skip this step [the check valve].” and “If the air pump is positioned lower than the top of the aquarium, you need a check valve to prevent water leakage through the airline tubing.” Heights differ by maker (Tetra 12”, hygger 25cm); our reading: follow your pump’s manual. Co-Op puts the valve’s flapper end toward the pump: “If you install the check valve backwards, no air will flow when you turn on the air pump, so just flip the check valve around.” Tetra: “To avoid possible electrical shock, do not immerse pump in water. If pump falls into the water, or otherwise becomes wet, do not reach for it until you have first unplugged it.”

Check everything, loop the cords, then plug back in

Tetra: “Carefully examine appliance after installation. It should not be plugged in if there is water on parts not intended to get wet.” and “Do not operate appliance if it has a damaged cord or plug, or if it is malfunctioning, or if it is dropped or damaged in any manner.” It says: “To avoid getting the appliance plug or receptacle wet, position the aquarium to the side of a wall-mounted outlet.” and “Arrange a “drip loop” for each cord connecting an aquarium appliance to an outlet.” The loop is “the part of the cord below the level of the outlet that prevents water from traveling along the cord and coming in contact with the outlet.” And: “If the plug or receptacle gets wet, don’t unplug the cord. Disconnect the fuse or circuit breaker that supplies power to the appliance. Then unplug the appliance and examine the outlet for the presence of water.” With hands out and parts in place, plug the filter and pump back in, and the heater as its manual says; Aqueon names “forgetting to plug it back in” as a risk of unplugging a heater.

Plants make oxygen by day and use it at night

The Spruce Pets says plants release oxygen by day, but “at night, this process reverses, causing plants and algae to consume oxygen”, and: “Adding a light or increasing the lighting duration during the day can help raise oxygen levels.” Aqueon: “Don’t leave the aquarium light on 24/7. This not only stresses your fish but can lead to excessive algae growth.” In hot weather, Aqueon says to “Turn off the aquarium light – or in the case of planted and reef aquariums, limit the number of hours the light is on – to help reduce heat generation.”

Retest

Test ammonia and nitrite again, and keep testing until both read zero. With a chemical additive, The Spruce Pets says to “err on the side of safety by increasing the tank’s water circulation for the duration of treatment so that it maintains sufficient oxygen.”