Saltwater Aquarium Maintenance: Topping Off Your Tank With Freshwater

Aquarium Maintenance: Topping Off

When water evaporates from your saltwater aquarium, only the fresh water evaporates, and the salt is left behind. In order to maintain a consistent salinity level, we must top off our tanks with fresh water.

There are two ways to top off your tank, manually or automatically. Manual top off is simply adding reverse osmosis de-ionized water (RODI) to you tank, while automatic top off requires the use of a fresh wreservoirvoice and auto top off device. There are several types of automatic top off systems but they all work to replenish your tank with fresh water.

Manual Top Off

The first step is always to test your salinity before adding RODI. You can test your salinity using a hydrometer or a refractometer. Hydrometer are inexpensive, and great for getting started, however, you should invest in a refractometer and become familiar with using one. Refractometers are easy to use and give you a more precise reading.

Your Salinity reading should be 35ppt or 1.0264 specific gravity.

Hydrometers are good for starting out. Investing in a Refractometer will give you more accurate results.

Once you’ve tested your salinity and added some water, wait a few minutes and test again, repeat as needed until the salinity is 35ppt or 1.0264 specific gravity. If you are topping of manually you can pour this water directly into the top of your tank. We add water near the flow which quickly mixes the freshwater into the tank.

Automatic Top Off

If you are setting up an automatic top off system, you will need to have an auto top off reservoir which you keep within plumping distance from your main display.

maxresdefault — When topping off manually, it is a good idea to mark where the water line is supposed to be.

There are several automatice top off option on the market and they more or less work the same way. With auto top off you do not need to add water directly to your tank instead you only need to monitor the water level in your auto top off reservoir.

When you install an auto top off system in your tank, you first place a sensor inside your sump or filtration area in the back of your tank. When the water level falls below the sensor the auto top off pump will turn on and inject fresh water into the tank. You will also set a high water level which will cause the auto top off pump to stop.

This diagram shows the basic concept of automatic top off. — This diagram shows the basic concept of automatic top off with the reservoir on the left and aquarium tank on the right.

Automatic Gravity Fed Top Off

You can also use a gravity fed top off system with a float valve. When the water level dorps, the float drops and opens a valve whick lets water in the tank until it floats up again. With this system, your top off reservoir needs to be kept above your sump.

This is the type of valve you would use when setting up a gravity fed top off.

It is best to have a separate top off reservoir for gravity fed top offs, rather than plumbing your RODI water system directly to your top off. If the float switch system fails, then only the water in the dedicated top off reservoir will drain into your tank. If your float switch is plumbed in directly to an RODI unit you risk continually pumping in fresh water and overflowing your tank.

Remember to top off your tank and test your salinity as often as possible. There are countless ways to do things in this hobby so pick the way that is best fitted to you.

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