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How high should the water level be in your fish tank?

Just because you bought a 55 gallon tank, doesn’t mean that you have to completely fill it with water. In fact, filling your aquarium to the brim can cause more harm than good.

Benefits of loading your tank with water all the way to the top

The main benefit of filling your fish tank all the way up to the brim is that you get more water volume to work with. Larger bodies of water are better at diluting harmful toxins like ammonia, nitrite and nitrate. This will give you more leeway when it comes to maintaining the water quality as well as the health of your fish and other aquatic life. Furthermore, you also increase the surface area for your beneficial bacteria to grow.
Aside from being more healthy, the added water means that you can add even more fish if you so desire.

Disadvantages of filling completely filling your aquarium to the brim

The main issue we have with completely filling out your tank with water is that it could cause a mess. If you have a high water line, then there is a good chance that splashes made from your air stone, filter and/or fish can go over your tank. This will wet your stand, floor, electronics and other objects you have close to your tank.

The other problem we have is that it will be very easy to cause an overflow. Putting any object (such as substrate, rocks and decor) in your tank that has more mass than H20 will raise the water level. This include your arm if you are performing a water change and/or doing other maintenance.

Some tanks may also have black trims on the top. If you have fish that like to be on the surface of the tank, then it wouldn’t make sense to increase your water level beyond the trim as it will block your view anyway.

Not to mention that having a high water line will make it easier for fish or other aquatic life to jump/and or escape from the tank. Of course, no one wants to come home to see dead fish lying on the floor next to an aquarium.

Although you can solve the jumping issue by using a fish tank cover, you will also be cutting off the airwave if your water line is too high. This is because gas exchange occur in the surface of the water. If you have a top on, the amount of air is already limited. By filling your tank to the brim with water, you will further decrease the amount of open air in your aquarium.

How much should you fill your tank with water?

If you have a black trim attached to the top of your aquarium, then that is a good guideline to start with. The trim on our tank, which is a standard rectangle 55 gallon from Aqueon, takes up around 1.5 inches from the top. We actually prefer lowering the water line a little bit more by another inch as our filter and bubbler can create splashes that can go quite high.

So it’s best to experiment a little bit in the beginning and then adjust the water line to fit your needs. In general, having an aquarium top will prevent the splashes from going out of your tank, which should give you more leeway if you want to raise the water line.


If your water line is too high, you risk water overflowing and splashing out of your tank. Not to mention that you fish or other aquatic pets have a greater chance of escaping the tank. While you can use a top, doing so will restrict airflow to your aquarium.

We recommend leaving a couple of inches to start with. You can then adjust the water level to whatever fits your needs for your specific tank.