How to Use Epsom Salt for Your Fish Aquarium + 5 Benefits

There are several natural treatments for aquarium fish ailments, but Epsom salt (MgSO4) is a common favorite. Epsom salt is the household name for magnesium sulfate – a natural mineral with a white crystalline appearance. It has been used for decades to ease minor muscular soreness and constipation in humans, while being cheap and easy to find. Its use has extended to fish aquariums because of its potential benefits. This article will tell you everything you need to know.

Using Epsom Salts in Aquarium

The use of Epsom salts in aquariums is not well-researched or backed up by science. It’s mainly used as a minor treatment for common fish parasites or to alter the water parameters. It can be added to marine and freshwater aquariums but isn’t a good treatment for sensitive fish species. Epsom salt should always be used cautiously because it can be dangerous to fish if misused.

You only want to use food-grade Epsom salt in your aquarium. It should be refined and free from harmful chemicals, additives, essential oils, and perfumes which are harmful to fish.

Dosage

The safe dosages of Epsom salt in aquariums are debatable, but 1/8 teaspoon of Epsom salt is generally recommended for every five gallons of water. Adding too much Epsom salt in your aquarium can do more harm than good, so rather put too little in than too much. Never place Epsom salts into the main aquarium to treat fish diseases, as it can alter the water chemistry and kill sensitive fish. Rather use it in a separate aquarium setup solely to treat your sick fish.

If you accidentally add too much Epsom salt into your aquarium, you should perform partial water changes every few hours. Aim for 30% to 40% water changes every four to six hours to dilute the Epsom salts in the water. It is better to add the Epsom salts using an accurate measuring spoon rather than pouring it straight from the packaging.  

5 Benefits of Epsom Salts in Fish Aquariums

Let’s take a look below at the five potential benefits of Epsom salts for aquariums. Remember that its benefits are purely anecdotal and should be used at your own risk.

1. Raises General Hardness (GH)

When Epsom salt is added into aquariums, it breaks down into magnesium and sulfate ions. Hard aquarium water is naturally high in minerals like calcium and magnesium, so adding Epsom salt into the aquarium could raise the general hardness. However, it is best used alongside baking soda to have a noticeable effect on the water’s general hardness.

2. Coral and Invertebrate Mineralization  

Most marine corals and invertebrates require magnesium to metabolize calcium properly and for general health. Since Epsom salt contains magnesium, an essential macronutrient, it is believed that adding it to your coral aquarium can raise the water’s magnesium concentration.

Magnesium is abundant in seawater and plays an important role in the calcification of marine corals and similar invertebrates. Although there are various commercial magnesium products for marine aquariums, Epsom salt might be an affordable alternative.

3. Cleans Hard Water Stains

There are many tried-and-trusted methods to clean unsightly hard water stains from aquariums, but Epsom salt comes highly recommended. Mixing a solution of Epsom salt and baking soda in water and letting it sit on hard water stains can help make it easier to remove later on.

You ideally want to mix around two tablespoons of Epsom salt and baking soda in warm water to create a watery paste. Alternatively, you can use white vinegar and Epsom salt to clean stubborn hard water stains in aquariums.

The aquarium should have no live inhabitants inside during the cleaning process and the mixture can be harmful for them.

4. Parasite Treatment

There is a possibility that Epsom salt might be effective against certain internal and external fish parasites. It is thought to work by creating an unideal environment for the parasites to reproduce and live in. However, using Epsom salt to treat fish parasites is not recommended over appropriate fish medications. It should rather be used as a last resort after you have tried safer and more successful treatments.

There is no current evidence on which types of parasites Epsom salt is effective against, as each parasite usually requires a different treatment method.

5. May Aid In Aquatic Plant Growth

If you grow live plants in your fish aquariums, Epsom salt could be beneficial as a natural fertilizer. We already established that Epsom salt is a macronutrient containing magnesium, which is needed for plant growth. Despite this mineral compound’s name, Epsom salt is not actually a salt. Therefore, it does not risk dehydrating your aquatic plants or raising the waters salinity.

Does Epsom Salt Help Constipated Fish? Debunking The Myth

One of the most common uses for Epsom salt in aquariums is to treat constipated fish, specifically goldfish. The reason behind this is likely due to the laxative effect Epsom salt has on humans. However, the truth is that most fish cannot get constipated in the same way we do, making Epsom salt an ineffective treatment.

Fish live in an entirely aquatic environment with no chance of becoming dehydrated and ending up with dry stools. They also have vastly different digestive systems than humans and some fish lack similar organs.

In the case of goldfish that have no stomachs, there is a low possibility for them to become constipated in the first place. Their food quite literally passes right through their intestines and gets pooped out regularly. Water is constantly moving through their body and helping to keep their bowel movements regular.

What About the Clear, Stringy Poop?

If fish haven’t eaten for a while, they usually produce an empty poop casing that almost appears transparent. Although it might seem like this poop casing is a sign that they are constipated, it is quite normal and not usually a cause for concern. The poop casing is made of mucous which coats their poop and helps it pass through easily. Many factors influence how frequently fish poop, so water temperature and diet should be considered.

Why Does It Seem Like Epsom Salts Are Helping?

The reason your fish might poop more with Epsom salt in the water is likely from stress as they adapt to changes in the water’s chemistry. Furthermore, water quality may interfere with a fish’s digestion, leading to changes in their bathroom habits. The reasoning has little to do with Epsom salts’ laxative effect in humans, and more to do with changes in the water.

In Summary

Epsom salt is a mineral of magnesium sulfate and not a true salt. Its use in aquariums is anecdotal but believed to help raise the general hardness of the water and aid in certain parasitic fish treatments. Only food-grade Epsom salt containing 100% magnesium sulfate is recommended for fish aquariums. Epsom salt should only be dosed in low levels to risk harming your aquarium inhabitants. It’s best to be cautious about using it with sensitive fish, plants, and invertebrates.

The photo featured at the top of this post is © iStock.com/Leonid Eremeychuk