How High Does the Water Level Need to Be in an Aquarium?

For the most part, the fish keeping hobby adheres to the principle of working with all the water that aquarium tanks or garden ponds can hold. The idea of filling up a saltwater or freshwater aquarium with as much water as possible is based on dilution of substances that are toxic for fish, invertebrates, and plants. We’re talking about nitrate, nitrites, and ammonia. As long as you have the right aeration and filtering system, it’s actually easier to keep water quality at optimal levels when the volume is higher. Even with this water volume advantage, there are reasons you shouldn’t fill your tank all the way to the top.

Recommended Waterline

Many rectangular aquarium tanks have a plastic trim at the top that looks very similar to the base at the bottom. The base is more functional than the trim at the top because it’s meant to provide support and impact resistance, but a good rule of thumb related to the trim at the top is to use it as a waterline guide. You should generally fill the tank up to an inch below the trim because the water column and aeration system will create bubbles that splash the surface. When the waterline is too high, water may splash outside of the tank.

The Risk of Jumping Fish

Jumping behavior isn’t unusual among aquarium species. It’s often a defense mechanism that can help fish survive in their natural habitats. For example, Siamese fighting fish will jump whenever they sense a spike in ammonia levels. Gasteropelecidae like to swim close to the surface and may jump out of curiosity. Needless to say, a high waterline increases the risk of fish jumping out of the tank, but you should think about installing an aquarium cover or a net regardless of the waterline level.

Setting a Waterline for Emergent Plants

Seasoned aquarists will tell you that aquatic plants are crucial in the development of a healthy ecosystem. Planting a single Cryptocoryne that takes root in the substrate and continues to emerge closer to the surface will work wonders in terms of oxygenating the water and keeping algae bloom under control. If you have one of these emergent plants, you must keep in mind that it will seek to break the water surface so its leaves absorb air. For this reason, you should give it some room to grow happily. An amendment to the cover rule is that most freshwater planted aquariums are open on top.

Keeping a Paludarium

A paludarium tank is never meant to be filled to the top with water because it combines elements of aquatic and terrestrial ecosystems. This specialty hobby within the aquarium world allows keepers to stock their tanks with amphibian species such as frogs and tiny turtles. Plus, it also requires plants that grow above the water surface as they attach their roots to semi-submerged driftwood and rocks. We have a beautiful ADA paludarium at Aquatic Warehouse to enjoy as a sampling of what can be done.

In addition to maintaining the proper water level in your tank, there are several supplies you’ll need to ensure the aquatic environment is optimal for your fish and plant life. At Aquatic Warehouse, we carry everything you need to keep your aquarium running smoothly. Stop by our store in Kearny Mesa, check out what we have to offer on our website, and call us at 858-467-9297 if you have any questions.