Do Axolotls Need Salt? | How to Make Holtfreter’s Solution and Other Salt Recipes

Do axolotls need brackish water? Then why do axolotl websites always talk about Holtfreter’s Solution and other salt recipes? And why is it so hard to make them? In this article, I cover:

• Recommended pH, GH, KH, and salinity levels for axolotls
• Easy recipes for making Holtfreter’s, Modified Holtfreter’s, and John’s Solution (found on axolotl.org)
• The effect that salt solutions and aquarium salt have on pH, water hardness, and salinity

Recommended Water Hardness for Axolotls

First off, let's examine the axolotls' natural habitat. They come from high altitude freshwater lakes in Mexico City, but there’s not a lot of info how on what the water quality used to be like because nowadays the large lakes have been reduced to narrow canals and have been affected by pollution and runoff.

Comparison of axolotl habitat in 1500's versus 2000's (modified from Places Journal)

However, I did find a veterinary article titled Water Quality Explained: How It Can Affect Your Axolotl's Health written by Dr. Loh saying axolotls prefer a pH of 6.5 to 8.0 (ideally from 7.4 to 7.6). In other words, they like alkaline, or slightly basic, water.

GH (or general hardness) is usually what people mean when they say their water is hard or soft. Since the axolotl's natural environment is supplied from springs and mountain snow melt, the water picks up a lot of minerals, making it moderately-hard ranging from 7° to 14° GH.

KH (or carbonate hardness) is the measurement of your water’s buffering capacity or ability to keep the pH stable as acids and bases are added, so you generally don’t want it to be too low. According to Dr. Loh, axolotls need 3° to 8° KH.

As for salinity, Dr. Loh says it should be 0 g/L with a maximum of 15 g/L. So there you have it. It sounds like axolotls can live in low brackish waters, but freshwater is ideal.

How to Make Salt Solutions for Axolotls

Simplifying the Salt Recipes

If you look at the existing recipes for making salt solutions for axolotls, they're usually a little difficult to recreate because they're written in grams and require the usage of scientific scales (which most hobbyists don't own). Using a scale is a lot more accurate than using measuring cups and spoons, but after researching and recreating the salt solutions myself, I found that approximations using teaspoons (tsp), tablespoons (Tbsp), and cups (c) are sufficient for getting the proper salt ratios and buffering the water hardness levels. So with the help of a paper called Mass-Volume Equivalents of Common Chemical Solids, I converted all the recipes from grams into measuring spoon units for you.

The salt recipes on axolotl.org are also written for 100% concentration. However, typically we use a 40% concentration for axolotls and a 20% concentration for axolotl embryos. So I created the recipes to make a 40% concentration for the majority of use cases.

Recipe 1: Holtfreter's Solution

Materials

Calcium chloride

• 1.5 tsp calcium chloride
• 1.5 c non-iodized table salt
• 4 tsp potassium chloride
• 3 Tbsp baking soda
• 1 gallon of dechlorinated water
• 2- to 3-gallon water jug or dispenser

Instructions

1. Treat the 1 gallon of water with dechlorinator before using.
2. Pour some of the water in a large cup and mix in the calcium chloride first (as recommended by OceanBlue on Caudata.org). Pour the dissolved calcium chloride solution into the water jug.
3. Combine the rest of the dry components (i.e., table salt, potassium chloride, and baking soda) in a small bowl.
4. Dissolve some of the dry components with some water in a cup, and pour the solution into the jug.
5. Repeat Step 3 until all of the dry components have been dissolved. Pour the rest of the 1 gallon of water into the jug.
6. Close the lid of the jug and shake the solution very well before using. Add 1 c of salt solution into the aquarium for every 5 gallons of aquarium water to get a 40% concentration (or use 1/2 c of salt solution per 5 gallons of water for a 20% concentration). Make sure the aquarium is not filled to the brim or else adding the solution may cause it to overflow.

Recipe 2: Modified Holtfreter's Solution

Materials

Epsom salt

• 1.5 tsp calcium chloride
• 1.5 c non-iodized table salt
• 4 tsp potassium chloride
• 3 Tbsp Epsom salt
• 1 gallon of dechlorinated water
• 2- to 3-gallon water jug or dispenser

Instructions

1. Treat the 1 gallon of water with dechlorinator before using.
2. Pour some of the water in a large cup and mix in the calcium chloride first. Pour the dissolved calcium chloride solution into the water jug.
3. Combine the rest of the dry components (i.e., table salt, potassium chloride, and Epsom salt) in a small bowl.
4. Dissolve some of the dry components with some water in a cup, and pour the solution into the jug.
5. Repeat Step 3 until all of the dry components have been dissolved. Pour the rest of the 1 gallon of water into the jug.
6. Close the lid of the jug and shake the solution very well before using. Add 1 c of salt solution into the aquarium for every 5 gallons of aquarium water to get a 40% concentration (or use 1/2 c of salt solution per 5 gallons of water for a 20% concentration). Make sure the aquarium is not filled to the brim or else adding the solution may cause it to overflow.

Recipe 3: John's Solution

Materials

Water dispenser

• 6 Tbsp + 2 tsp non-iodized table salt
• 2.5 tsp baking soda
• 3.5 tsp Epsom salt
• 1 gallon of dechlorinated water
• 2- to 3-gallon water jug or dispenser

Instructions

1. Treat the 1 gallon of water with dechlorinator before using.
2. Combine all the dry components (i.e., table salt, baking soda, and Epsom salt) in a small bowl.
3. Dissolve some of the dry components with some water in a large cup, and pour the solution into the jug.
4. Repeat Step 3 until all of the dry components have been dissolved. Pour the rest of the 1 gallon of water into the jug.
5. Close the lid of the jug and shake the solution very well before using. Add 1 c of salt solution into the aquarium for every 5 gallons of aquarium water to get a 40% concentration (or use 1/2 c of salt solution per 5 gallons of water for a 20% concentration). Make sure the aquarium is not filled to the brim or else adding the solution may cause it to overflow.

Recipe 4: Aquarium Salt Solution

Materials: aquarium salt

Instructions

1. Follow the instructions on the aquarium salt container. For the API brand, it said to use 1 rounded Tbsp of salt per 5 gallons of aquarium water.
2. Dissolve the salt in a cup of dechlorinated water first and pour into the tank.

Results: Effect of Salt Solutions on Water Hardness

After creating the solutions and adding them to 5 gallons of distilled water, I measured their pH, GH, KH, and salinity. Tools I used included the pH test kit, high range pH test kit, GH and KH test kit, and a refractometer. Here are the main effects of the salt recipes I tested had:

• Baking soda in Holtfeter’s solution raises KH and PH in distilled water.
• Epsom salt in Modified Holtfeter’s Solution raises GH.
• John’s solution had both baking soda and Epsom salt, which raised the pH and then increased the GH and KH by a little bit.
• Aquarium salt did nothing noticeable
• Salinity didn’t budge with any of the solutions! Even all that NaCl wasn’t salty enough to be measured by the refractometer.

My tap water actually has 8 pH and 3° GH and KH. It meets the lower limit of KH but is way below the recommended GH, so if I was going to use a salt recipe, I’d go for the Modified Holtfreter’s Solution that uses Epsom salt and doesn’t affect pH. Or I'd use John's solution but increase the Epsom salt to 3 Tbsp like the Modified Holtfreter's recipe.

Conclusion: Is It Worth It?

So would I add dissolved salts to my axolotl tank? Mmm… maybe? Developmental Biology of the Axolotl is the definitive textbook on axolotls, and it says on page 223:

Even though axolotls are freshwater amphibians, many laboratories find that they thrive best in a dilute saline solution [such as the Modified Holtfreter's solution that they use]... The saline seems to reduce fungal and bacterial growth, and the animals seem healthier than in straight tap water.

However, remember that the laboratory environments change 100% of the axolotls' water everyday, whereas the average axolotl hobbyist (like me) rarely does 100% water changes. So I’d be mainly concerned about keeping consistent levels of pH, GH, and KH every time I do a partial water change.

Plus, I use evaporative cooling to cool my axolotl tank, which means the mineral concentration would constantly keep creeping up as the water evaporates. In order to maintain the correct mineral levels, I’d have to keep buying and topping off the tank with distilled water (or buy an RO/DI unit to make my own purified water). Constantly fluctuating water parameters is very stressful for animals, which can cause a weakened immune system and health issues in the long run.

There are other methods of increasing your GH and KH without constantly having to dose buffering solutions. You can use limestone or put a bag of crushed coral in your filter, but cichlid keepers have more experience in this area than me so check out some of their forums.

Question of the Day

Do you use salt with or buffer your axolotl’s water? Comment below to share your experiences. To learn more about axolotl care, check the short playlist I’ve put together for you. Don’t forget to take time to enjoy your aquariums and I’ll see you next time!

---

Subscribe to my YouTube Channel for practical fish care tips for busy aquarists and follow me on Instagram for daily updates! 🎮❤️🐟