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Creating DIY Live Rock for Saltwater Aquariums (8 Simple Steps)

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By Lindsey Stanton


If you’re considering setting up a saltwater aquarium, one of the best ways to get your tank started up is live rock. Live rock is highly porous and is an excellent way to introduce beneficial bacteria to your tank. It also creates a base for the placement of corals and some plants.

Live rock can be pricey, upwards of a few dollars per pound, and natural live rock is often detrimental to the ocean. Natural live rock removed from the ocean takes organisms and a growth point for corals and anemones with it.

The good news is that you can make your own live rock! It’s more eco-conscious and cost-effective than purchasing live rock. It’s a time-consuming project that requires patience, but it isn’t a difficult project. Here’s what you need to know about creating your own live rock for your saltwater aquarium.

aquarium plant divider

What is Live Rock?

Natural and artificial live rock are usually made from aragonite, which is a form of calcium carbonate. Corals and other creatures use the calcium from the aragonite to grow and as they die, the calcium from their decay helps grow the aragonite.

The porosity of live rock creates high surface area, which allows for the colonization of beneficial bacteria. Since live rock is made from calcium carbonate, its presence can raise the pH and hardness of your tank, making a better environment for saltwater creatures.

Supplies You’ll Need:
  • Concrete mixing container
  • Mold making container
  • Fine aragonite sand (to fill mold container)
  • Coarse aragonite sand (for live rock)
  • Portland cement
  • Distilled or reverse osmosis water
  • Rock salt (optional)
  • White vinegar (optional)

aquarium plant divider

Creating Your Own DIY Live Rock

1. Make a plan

Make sure you get all of your supplies together in one place before starting this project. The concrete will begin to set relatively quickly, so you will need to be able to work fast. Once you start mixing and filling molds, stepping out for a quick trip to the store for more supplies won’t work. Plan how much live rock you want to create and make a general idea of the size and shape of rock you want.

wet concrete mix
Image Credit: chomplearn, Shutterstock

2. Prepare the molds

Fill the molding containers with the fine aragonite sand and dampen it so that it is moldable. Think of the consistency of the perfect sandcastle building sand; that’s the consistency you’re going for. Dig out a mold in the size and shape you are wanting your live rock to be. Get creative! You can use small filled balloons to make caves and swim-throughs, you can use rolled up news paper or balloon animal balloons to create tunnels. Whatever you use should be able to be easily removed and not leave trace chemicals behind. You can also use things like clean PVC pipe to create tunnels but do that knowing that it will be a permanent part of the rock.

3. Mix the components

Once your molds are ready, you’re ready to start mixing your coarse aragonite and concrete into a mixture called aragocrete. How you mix this is partly up to your personal preference, but you will want to at least use a 2:1 aragonite to concrete ratio. Depending on the texture and look you’re going for, you can do up to 8:1 or possibly even higher. At this point, you can also mix in the rock salt if you choose to use it. This will help create more texture and porosity in your rock and will dissolve away during the curing step.

4. Fill the molds

Once you’ve created an aragocrete mixture that’s a handleable consistency, you’re ready to fill your molds. Scoop the aragocrete into the molds you’ve created in the aragonite sand, making sure you fill the crevices. Once you’ve filled your mold, top with additional aragonite sand, covering the aragocrete completely.

aquarium with filter
Image Credit: Dovzhykov Andriy, Shutterstock

5. Let sit

Now it’s time to not touch anything for about 48 hours. Don’t be tempted to move the sand to check how the rock is setting. Just let everything sit in a dry environment that is protected from the elements. If it’s very cold or very humid outside, then a garage without climate control isn’t a good option.

6. Rinse and cure

After your rock has set for at least 48 hours, it should be fully set. Dig your newly formed rock out of the sand, remove anything you’ve put into the rock, like balloons or paper, and rinse the rock well to knock off the loose sand. You can keep the loose aragonite sand in your mold making container for future live rock projects. At this point, you’ll need to allow the newly made rock to cure to prevent chemicals from the concrete leaching into your tank and potentially permanently altering the pH. You can cure the rock by soaking it in freshwater for around a year or you can cure it by soaking the rock in vinegar water for around a week. If you do the vinegar water soak, you’ll need to change the water out daily.

7. Seed the rock

After your rock has fully cured, it’s just a rock, not a live rock, because it doesn’t have bacteria colonies. You can colonize it by adding saltwater creatures, like corals, snails, anemones, and other animals that will produce waste and feed from the calcium in the rock. Scraping coralline algae from surfaces within your tank and applying to the new rock is an excellent seeding technique. You can also put the new live rock where it is touching seeded live rock, or even just put it into a tank with established bacteria colonies.

8. Enjoy your work

Once your rock is cured and seeded with beneficial bacteria, it’s ready to be used in your saltwater aquarium. Sit back and enjoy your work!

man cleaning aquarium using magnetic fish tank cleaner
Image Credit: hedgehog94, Shutterstock

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In Conclusion

Live rock is a necessary part of reef tanks and is a beneficial part of other types of saltwater tanks. For people who are environmentally conscious, finding live rock that doesn’t have a negative impact on the environment can be difficult. Making your own live rock provides a more eco-conscious means of having live rock in your tank.

Making your own live rock will take you multiple days, and potentially a year depending on how you choose to cure your rock. In the end, though, your patience and time will pay off and your tank will be happier and healthier with the addition of a porous, saltwater friendly rock that provides a home for invertebrates and beneficial bacteria.

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Featured image credit: Petrychenko Anton, Shutterstock

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