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Which magnets should I pick for use in an aquarium?

Waterproof magnets are your best choice for use in aquariums. They are neodymium magnets inside a rubber casing, and with the help of these magnets, you can attach pumps, reef rock, coral frag racks, thermometers and more to the glass of your aquarium. Suction cups that won’t stick are now a thing of the past. However, unprotected neodymium magnets are not recommended for permanent use in water because they will start to rust. On this FAQ page, we have put together a variety of information that is of interest to you as an aquarium enthusiast.
Table of Contents

Suitable magnets for aquariums

If you want to use magnets in your aquarium, then waterproof magnets are recommended. Thanks to the rubber coating, the neodymium magnets on the inside are protected from moisture. This protective casing also prevents scratches on the aquarium glass.
Important: Check the coating of the rubberised magnets for damage before using them in the aquarium. The magnet on the inside will only be protected with an intact casing.

Finding the right magnet for your aquarium

To find the right magnet, several factors need to be taken into account. Among them are:
  • The weight of the object to be attached
  • The thickness of the aquarium glass
  • Mounting of the magnet on a horizontal or vertical surface
Find out below what you need to keep in mind for each of these different factors.

Weight of the object to be attached

Even though the magnets in our shop are super strong, there is a limit to how much they can hold. That is why, as a first step, you should always determine the weight of the item you want to mount inside the aquarium. Next, you need to find a magnet with the right strength.

Mounting on a horizontal or vertical surface

Another crucial aspect is whether the magnets are to be attached on a horizontal or vertical surface. For a horizontal surface, you need to consider the ‘adhesive force’ whereas the ‘displacement force’ needs to be taken into account for a vertical surface. These values are included on the respective product pages. If, for example, you want to use magnets to mount a pump on the glass pane (i.e. on a vertical surface), you will have to factor in the displacement force. It is usually 1/5 to 1/6 of the adhesive force.
Please note: These values only apply if the magnets are in direct contact with one another. The force is significantly lower when magnets attract each other through aquarium glass. See the next section below for more information.

Thickness of the aquarium glass

To mount a magnet on the inside of the aquarium, a second magnet (or a ferrous counterpart) must be attached to the outside. The thickness of the aquarium glass will dictate the strength of the magnets you need because the force of the magnets decreases rapidly as the distance between them increases. Already a distance of just one millimetre reduces the magnetic force significantly. You can learn more about this topic on our FAQ page What factors affect the adhesive force and strength of a magnet?.
To determine how much adhesive force the magnets develop on your aquarium glass pane, you can utilise our online adhesive force calculation tool.
But please keep in mind: Since waterproof magnets cannot be used for these tool calculations, it is best to look for a regular neodymium magnet in the online shop that closely matches the size and strength of the waterproof magnet. For example, the rubberised magnet S-20-10-R (adhesive force: 7,1 kg, displacement force: 1,4 kg) is pretty close to neodymium magnet S-20-10-N (adhesive force: 11 kg, displacement force: 2,1 kg). So you can select that neodymium magnet in the online tool. Next, add 2 mm to the thickness of the aquarium glass to account for the rubber coating of the waterproof magnets. Enter that value in the ‘Distance’ field and start the calculation.

Specific example: Mounting an aquarium pump

To help you, we will give you a specific example. Let’s assume that you want to attach an aquarium pump to the glass of your aquarium. You already know the following:
  • The pump weighs approx. 500g
  • The glass is approx. 10 mm thick
  • Rubber-coated magnets on both sides of the glass will hold the pump
  • The coating of the rubberised magnets is 1 mm thick
  • For the calculations, the displacement force has to be taken into account
When being in direct contact, many of the waterproof magnets have a low displacement force and are therefore too weak for your project. That is why you perform the calculations in the adhesive force tool using a rubberised magnet that is as strong as possible. Hence, S-20-10-R is the magnet of your choice. As mentioned above, to process the calculations in the online tool you will have to find a neodymium magnet with identical shape and similar properties and so you pick S-20-10-N.
Thanks to the adhesive force tool you find out that, at a distance of 12 mm, two magnets type S-20-10-N still have an adhesive force of approx. 1,2 kg. Using a calculator, you now determine the displacement force (between 1/5 and 1/6 of the adhesive force) and learn that the remaining strength is about 200 to 240 grams per magnet.
For you, that means: A single magnet type S-20-10-N is not enough to mount your aquarium pump. Your project requires at least 3 S-20-10-N magnets on the pump and 3 magnets of the same type as counterparts. Together, they have a total strength of 600 to 720 grams.

Can I use waterproof magnets in saltwater?

The coating of rubberised magnets is 100% saltwater-proof. You can therefore use these magnets in a saltwater aquarium since the casing will not turn brittle.

Does the coating of a waterproof magnet release harmful substances into the water?

Our rubberised magnets are coated with TPE (thermoplastic elastomer), which does not contain any plasticisers like other synthetic materials. However, we do not have further detailed information or empirical values as to whether other harmful substances get into the water of the aquarium.

Tip: Use magnets to remove algae from the aquarium glass

One of our customers submitted the application Cleaning the aquarium where he explains how he fashioned his own magnetic tool to clean the glass panes. Keep in mind that stronger magnets may be required depending on the thickness of your aquarium glass.

Safety information

As with other applications, the following also holds true for aquarium use: Be careful when handling the magnets. This is especially relevant for neodymium magnets with a high adhesive force.

Do not let strong magnets collide with each other as they could shatter. In a worst-case scenario, this would not only damage the magnets but also the aquarium glass. Also, be careful not to pinch your fingers (or worse, your fish) between two magnets, as this could lead to injuries or bruises. We recommend that you familiarise yourself with the safety information for neodymium magnets before handling the magnets.