Neodymium magnets are typically plated with nickel to prevent rust and corrosion that results from moisture, but unless protected with a special corrosion-resistant coating, they are not waterproof.
Nickel-coated neodymium magnets are usually referred to as indoor magnets. They should be kept away from water (especially salt water), as exposure to moisture can cause them to corrode and lose their magnetic strength over time. This is because neodymium magnets have a very high iron content of 64 to 68 percent, making them notoriously susceptible to corrosion, especially in damp environments.
Corrosion will affect the strength of the magnets, especially if they rust, which causes an air gap. This will produce an insecure bond for ferromagnetic materials. Also, if magnets get wet, it can cause the laminate to bubble.
It is also important to note that even a small amount of water, such as high humidity, can cause rust to form on the surface of all nickel-plated neodymium magnets over time.
So the bottom line is: If you need to use neodymium magnets in a damp or wet environment, it is best to use them with a corrosion-resistant or waterproof coating or within a waterproof sleeve or container.
Since water is almost completely non-magnetic, it doesn’t significantly impact a magnet's performance. Magnets don’t demagnetize, and you get the same magnetic field and pull force from a magnet underwater that you get out in air or in a vacuum.
Researchers have also found that when a permanent magnet is kept in contact with water, the water gets magnetically charged and acquires magnetic properties. In addition, data shows that magnets actually behave with a slightly stronger pull force in colder water, down to minus 103 degrees Celsius.
Neodymium Magnets in Aquariums
Neodymium magnets are used in aquariums for their ability to attract to one another through glass and walls. Most aquarium applications consist of two magnets attracting toward one another, with one inside the tank walls and one on the outside.
Again, the magnets will attract to one another underwater. The biggest concern with using neodymium magnets in an aquarium is corrosion. In the presence of moisture, neodymium magnets can rust about as fast as a piece of raw iron.
While the nickel plating does slow this down, the nickel eventually loses the battle. What’s worse, rusting magnets may harm aquatic life. So, do not put unprotected magnets into your aquarium!
Our epoxy-coated magnets and plastic-coated magnets offer a safe, convenient solution. But which ones will work best?
The key to choosing the right magnets is knowing the wall thickness the magnets will have to reach through. For most smaller aquariums with 1/8-inch thick glass walls, a pull force of 4 - 8 pounds is about right for wall cleaners and coral frag holders.
The farther apart magnets are from one another, the weaker the pull force between them will be. As a result, magnets that work well on a small 10 - 20 gallon tank with 1/8-inch thick walls will not be strong enough for a bigger tank with 3/8-inch or 1/2-inch thick walls.
Neodymium Magnets and Salt Water
A magnet placed near or in salt water will continue to attract magnetic objects in the water. So far, so good.
But, as we’ve said, magnets typically react to moisture by rusting. Whether a magnet is fully immersed in salt water or simply operating in salty air, this exposure can cause even more serious corrosive damage to weaken the magnet’s strength. The idea would be to get the right corrosion-resistant coating when your magnets are used in and around salt water.
Also, fishing magnets are now available to drop into the ocean, as well as into all of the ponds, lakes, lagoons, reservoirs, and rivers near you. These magnets, often called retrieving magnets, work extremely well in picking up objects containing iron that have fallen into the water. This can be a lifesaver if your keys fall into a pool infested with sharks, piranhas, or alligators.
These fishing magnets, which are usually only nickel coated, must be thoroughly cleaned and dried after each use to maintain their long-term integrity.
Plus, what else can happen when you put magnets into the sea? For one thing, neodymium magnets are known to repel sharks. Studies show that these magnets interfere with a shark’s ability to sense electrical fields. In addition, a recent study showed that neodymium magnets placed on large fishing nets can repel sharks and other aquatic predators from entering the trap.
Waterproof and Corrosion-Resistant Coatings
So whether you’re working in an aquarium and/or in a salt water environment with magnets, here is a list of the neodymium magnet coating options we’ve alluded to above:
Epoxy Coated Magnets - The epoxy coating on these neodymium magnets provides superior performance in humidity and water - with excellent performance in salt water and salty air. The one downside to the epoxy coating is that it is not very abrasion resistant and can be very easily scratched.
Plastic Coated Magnets - These magnets are coated with a 1mm thick layer of ABS plastic, providing a waterproof seal. The plastic protects the magnet from moisture and prevents damage to the magnet itself. This coating provides superior performance in all water environments and is also very durable.
Electroless Nickel Magnets - An electroless or chemical nickel coating is a protective layer that is applied to a magnet without an electrical current. Instead, this coating is applied with a chemical bath that deposits the nickel onto the surface of the magnet. Thicker and more expensive than other coatings, electroless nickel-coated neodymium magnets work well in outdoor and humid environments with superior corrosion resistance. To learn more, read about the differences between Nickel vs Electroless Nickel.
Sewing Magnets - These magnets are encased in a waterproof PVC pouch that protects them from moisture. The PVC pouch also enables the magnets to be sewn into fabric or other materials to offer a durable and dependable long-term waterproof hold.
Do not use rubber-coated magnets underwater. Natural rubber can have tiny pinholes and may deteriorate over time.