Why use an aquarium without a cover?
An open-top aquarium lets plants grow out of the water, provides a direct view of the surface, and makes maintenance easier. In return, water evaporates faster, and some fish may jump. It is an excellent choice for a planted aquarium in a well-ventilated room with calm fish. With jumping species, a curious cat, or young children, keep some protection.
1 to 2 L/dayevaporation cited for a 60 cm tank
5 to 8 cmwater level below the rim
20 to 30 cmlamp above the water
Why remove the lid
The first reason is visual. Without a frame or hood, the eye looks over the glass, and the tank looks more like a piece of landscape. A root can protrude from the water and plants can grow in the air. This is why these aquariums are often found in aquascaping, as we remind in our article on choosing an aquarium.
The second reason is practical. Feeding, removing a leaf, pruning, or adding fertilizer is done without dismantling anything. A hanging lamp can also be moved during maintenance. It heats the water less than a closed hood, according to the testimonials collected by The Krib.
Finally, some plants benefit from this freedom. Gensou cites Hygrophila pinnatifida, Staurogyne repens, Rotala, as well as Anubias and Bucephalandra attached to a protruding piece of wood. Their aerial foliage changes the look of the tank, provided the air in the room is not too dry.
The drawbacks
- Evaporation. A lid reduces it, especially over large water surfaces. Gensou cites 1 to 2 liters per day for a 60 cm tank, in a room air-conditioned to 24 or 25 °C. On The Krib, one aquarist reports about double what they lost under a hood. These are guidelines, not measurements valid in your home.
- Jumping. Closed glass keeps fish in, an open tank does not. The risk increases with surface species, stress, and overpopulation, CO2Art explains.
- Humidity. Over several hundred liters, evaporation can promote mold on nearby walls, especially in a poorly ventilated room. CO2Art then advises keeping a lid.
- Dust and animals. Lids stop hair and dust. A cat can also have access to the water.
- Temperature variations. A lid dampens them, which matters for sensitive species.
Evaporation does have an advantage in summer: it helps dissipate heat. Our article on cooling an aquarium explains how to use it.
Common misconceptions
We often read that an open tank provides more oxygen. The aquarists of The Krib judge this difference to be very small, if not non-existent. This is not a good reason to remove a lid. If your fish lack air, look at the surface movement and the tank load. Our article on knowing if the aquarium is sufficiently oxygenated will guide you.
The same goes for the room light: it remains much weaker than that of a light bar. Opening the aquarium therefore does not replace suitable lighting. To size it, see which LED lighting to choose.
Succeeding with an open-top tank
- Lower the level. Gensou advises staying 5 to 8 cm below the rim to limit jumping.
- Suspend the lamp. 20 to 30 cm above the surface is a common guideline. Higher up, the light is distributed better but loses strength.
- Choose calm fish. Avoid danios, many killies, and certain rasboras, or place an almost invisible net.
- Add floating plants around the edges. They reduce the free surface.
- Mark the normal level and top up before the pump or heater ends up out of the water.
Be careful with the last point. Water that evaporates leaves its minerals. If you always top up with the same water, the hardness gradually increases. Therefore, control the GH and KH, as explained in our article on GH and KH, and keep a 20 to 25% weekly change.
Before leaving for several days. An open tank loses water even without you. Top up just before leaving and ask someone to check the level. Our article on managing the aquarium during holidays gives the procedure.
Choosing your aquarium
If you are starting from scratch, take a tank designed for this. The Oase ScaperLine range comes without a lid, with polished beveled edges and Optiwhite glass, according to our sheets. The set adds a matching cabinet. For an existing aquarium, first check what the lid holds: lighting, filter, or cables.
ScaperLine 60 Aquarium, 75 LBeveled edges and Optiwhite glass, designed for aquascaping.View productScaperLine 60 Black Set, 75 LAquarium with matching cabinet and tool storage.View productJBL Biotopol 500 mlWater conditioner for your top-ups and water changes.View productSera Aqua-Test SetTo monitor GH, KH, and other parameters.View product
Before buying, try it at home: remove the lid from your current tank for a week, if its lighting allows, and note the drop in level. You will then know how many top-ups await you, without relying on a figure taken elsewhere.
Are you hesitating about your room or your fish? Send us the size of the tank and its population.
Ask my questionFrequently asked questions
Is an open-top aquarium dangerous for fish?
Not inherently, but some species jump. Avoid fish known for this, such as danios, many killies, and certain rasboras, or place a fine net. Also lower the level by a few centimeters.
Does the water evaporate a lot?
Yes, significantly more than with a lid. Gensou cites 1 to 2 liters per day for a 60 cm tank in a room air-conditioned to 24 or 25 °C. The loss depends on your room: mark the level to measure it.
Does an open top provide more oxygen?
Not significantly. The testimonials from The Krib judge the difference to be very small, if not non-existent. It is the surface movement that matters most. Therefore, check the filter output, covered or not.
What water to use to top up evaporation?
Use water treated with a conditioner, at the tank temperature. Evaporation leaves the minerals in place: therefore, monitor the GH and KH, and keep your 20 to 25% weekly change.
Can you remove the lid from any aquarium?
No. On some aquariums, it holds the lighting or the filter. Check the manual before removing it, and keep a lamp designed to be suspended, away from water splashes.
Also read
To compare aquariums: What to choose as an aquarium? How to choose an aquarium?
READ THE ARTICLE
Sources and references
Last updated: November 4, 2026.
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