Aquarium lid: stop evaporation (and flying fish)
An aquarium lid cuts evaporation by 70 to 90 %, stops fish from jumping, keeps the heat in and shields the lighting from splashes. An open-top 100-litre tank loses 1 to 3 litres a week, more in winter above a radiator. Expect 15 to 60 € depending on the option you choose.
Why is evaporation a problem?
Because water evaporates pure: the minerals, nitrates and pollutants stay behind and concentrate. Keep topping up without changing water, and the hardness creeps up unnoticed. Evaporation also costs you in heating: an open tank loses its warmth through the surface and makes the heater run far more often, a point covered in our aquarium heater guide.
Which fish actually jump?
More than you’d imagine: killifish (legendary jumpers), bettas, gouramis, danios, swordtails, loaches — even a panicked neon tetra. A fish found dried out on the floor is one of the most common and most avoidable beginner losses. If your stock includes even one known jumper, the lid is not optional.
Glass, full hood or net: which to choose?
- Kit hood (plastic with built-in lighting): supplied with kits, practical, with feeding hatches. Replacement: 30 to 60 €.
- Custom-cut glass (15 to 40 €): cut by a glazier or ordered online, resting on clip-on supports. Sleek, and lets light through from a fixture placed on top.
- Mesh screen lid (20 to 35 €): the go-to for open tanks with a suspended light; stops jumpers without blocking gas exchange or light.
- Criteria: tidy cut-outs for cables and hoses, a feeding hatch, and easy removal for weekly maintenance.
How should you replace evaporated water?
Top up with low-mineral water, ideally pure RO water: added to replace water that left without its minerals, it keeps the hardness stable. Always topping up with tap water, by contrast, pushes the GH up month after month. Mark the reference level on the back pane and top up weekly before it drops too far: the heater element must never be exposed. More smart equipment in the accessories category.
Frequently asked questions
Doesn’t a lid block oxygenation?
No, as long as it isn’t airtight: the layer of air under the lid refreshes itself through the openings. Surface agitation from the filter does the rest.
Does a glass lid reduce the light reaching the plants?
Clean glass absorbs less than 10 % of the light. Wipe it weekly: limescale and algae can block far more.
My lid’s cut-outs are too wide — what can I do?
Fill the gaps with cut pieces of acrylic sheet or filter sponge: jumpers always find the one available hole.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.