How Much Live Rock Per Gallon (Calculator & Guide)

Mrbrefast, CC BY-SA 3.0, via Wikimedia Commons
Mrbrefast, CC BY-SA 3.0, via Wikimedia Commons

How Much Live Rock Per Gallon (Calculator & Guide)


Live rock is one of the most beneficial pieces that you add to your saltwater aquarium. However, where do you start and how much do you even need to support the creatures in your saltwater aquarium? Keep reading to learn more about one of the most foundational pieces to your reef tank’s ecosystem. 

How much live rock per gallon

The general rule of thumb for how much rock do I need per gallon of water? You can follow the suggested guideline of 1 -1.75 pounds of rock per gallon of water but this method is not 100 percent full proof. The density of your rock will change this distribution. For instance, a 30-gallon tank might require 17- 30 pounds of live rock per gallon. If you don’t think you want or even need that much live rock, you can fill in some space with dry rock.

Overall, it is important to know that the pounds of live rock that you may need per gallon will be different and dependent on how much of that bacteria you want to help in the natural filtration.

Common aquarium sizes and suggested live rock amounts

How much live rock for a 5-gallon aquarium?

5 to 8.75 pounds of live rock.

How much live rock for a 10-gallon aquarium?

10 to 17.5 pounds of live rock.

How much live rock for a 20-gallon aquarium?

20 to 35 pounds of live rock.

How much live rock for a 29-gallon aquarium?

29 to 50.75 pounds of live rock.

How much live rock for a 30-gallon aquarium?

30 to 52.5 pounds of live rock.

How much live rock for a 40-gallon aquarium?

40 to 70 pounds of live rock.

How much live rock for a 55-gallon aquarium?

55 to 96.25 pounds of live rock.

How much live rock for a 60-gallon aquarium?

60 to 87.5 pounds of live rock.

How much live rock for a 75-gallon aquarium?

75 to 131.25 pounds of live rock.

How much live rock for a 90-gallon aquarium?

90 to 157.5 pounds of live rock.

How much live rock for a 100-gallon aquarium?

100 to 175 pounds of live rock.

How much live rock for a 120-gallon aquarium?

120 to 210 pounds of live rock.

How much live rock for a 150-gallon aquarium?

150 to 262.5 pounds of live rock.

How to add and set up live rock in a saltwater tank?

You have your live rock but now you need to get it set up in your display tank but how do you do that? Live rock has a lot of benefits for your tank but they can only occur if you take your time and ensure that the rock is ready for the tank’s environment. There are two methods for curing your live rock: one method is for curing the live rock before the tank is set up while the other method is for after the tank has been set up and fish are already swimming in it. For our purposes, we will be focusing on the method that assumes you are beginning to set up your reef tank for the first time so there aren’t any critters yet.

  1. Fill your tank with properly mixed saltwater and aim for a specific gravity of at least 1.023 and a temperature that ranges between 72-78 degrees Fahrenheit. 
  2. Take a bucket of saltwater (preferably from the same supply that you are using for the display tank) and rinse your live rock pieces. As the pieces are sufficiently rinsed, you can begin to add them to your display tank. Keeping lighting off or dim to prevent algae growth during this process.
  3. Remove waste and other organic matter from the rock with a brush every few days.
  4. You will want to do water changes of at least 50 percent of the water weekly for the first few weeks. You will need to collect any other waste material that may be left in the tank with a siphon.
  5. Keep up with your water quality measurements and keep a log of the records.

The curing process should take around 2-4 weeks to complete. The water quality measurements will help you to know when the tank has stabilized.

Additional Note - Live Rock Hitchhikers

I have mentioned the pesky hitchhikers that can enter your tank by catching a ride on your live rock, well now is the time to begin to watch out for any of these pests. The sooner you identity and work to rectify the problem the better off you will be. The worst thing that you could do would be to not notice that Aiptasia has entered your tank and give it time to multiply.

Can you put too much live rock in an aquarium?

You can have too much live rock in a couple of ways. First, you can have diminishing returns the more live rock that you try to introduce into your tank’s system. There is little reason to have a tremendous amount of rock as it will make other things like space and flow much more of a problem for you to work around. The more live rock that you have in your tank the more flow blocks you could potentially introduce which will create dead spots in your tank. Plus, you probably want fish and other creatures to be the main attraction of your tank and not a bunch of rocks.

Live rock can be host to hitchhikers like Bristle Worms and Aiptasia which can create a host of problems for your fish and coral. The more live rock you add the more likely one of these pests finds a way in but you can help to diminish the chance of one of these pests from entering your reef tank. You should always inspect the live rock before your begin to acclimate it to your reef tank. You will find most of these pests if you keep an eye out. 

Do you need live rock to start a saltwater tank?

Not necessarily but that means that you will need to compensate for the lack of natural filtration within your reef tank. If you decide the rock is too much work or you don’t like the look of it then make sure you look at other filtration systems and sumps to make up the difference. Speaking of sumps, which are filtration systems that are in another smaller tank outside the display tank, you can always put live rock in the sump. That way the organisms on the live rock are still being introduced to your reef tank’s system and you can have the live rock out of the display tank. A win-win if aquarium live rock doesn’t jive with your overall aesthetic. 

Does the rock need a light source?

The live rock itself does not necessarily need light so if you are just trying to introduce your rock to your display tank then it is okay. You wouldn’t need light either if you put your live rock in the sump tank. It can just chill in there while you spend all your efforts lighting the display tank.

Light helps in algae growth so depending on the stage you are in introducing your rock to the tank’s system. Initially, it might be a good idea to keep light to a minimum.  

Why do I need live rock?

Live rock is extremely beneficial to the overall health of your reef tank. The ocean is made up of lots of tiny organisms that shape the water quality and make the ecosystem that fish are used to and that is the key. These organisms that take up residency in the live rock help aquarists replicate an ocean environment better. 

How do they do this? The beneficial bacteria are actually a crucial part of the nitrogen cycle that occurs in your saltwater aquarium and helps to detox the water quality for your fish. You fish and other creatures produce waste which creates its own chain reaction of chemical imbalances. The organisms in live rock essentially help to process that waste. The bacteria isn’t the end all be all of the tank maintenance but they can have a significant impact than if you were not using their natural abilities for yourself.

Dry rock is the same except it doesn’t have the bacteria that is conducive to the overall health of your saltwater aquarium.

How much is live rock?

Live rock isn’t the cheapest addition to your tank as most pet stores or online retailers will charge as high as 15 dollars for a pound of live rock. The price can be lower but the pounds add up and you can pay an extravagant amount of money on a live rock alone if you have a large enough tank. However, if you are more interested in the look of live rock rather than the little helper that live in its pores then you might consider just adding dry rock. Dry rock is much cheaper than live rock with the high end of the sellers selling their products at 5 dollars a pound. That is significantly cheaper but you are losing out on those filter organisms but if you are prepared for that, the dry rock may be the way to go. 

You could even use both! That way you can save some money but you aren’t losing out entirely on the benefits of live rock.

How long does the rock last?

As long as you take care of your live rock, it can last indefinitely. The main worries you will need to watch out for are pests like the Bristle Worm creating holes in your live rock. If you ever do a complete water change, you will need to be careful not to hit the rock and cause structural damage to it or surrounding rocks. 

However, the longer this rock is out of the water the more bacteria will die off. This is why many aquarists will opt for next-day delivery on their orders so they can mitigate the total loss of bacteria in the rock.

Final thoughts

Live rock is a great foundation for any great reef tank display due to the beneficial bacteria that live in the rock. Now you hopefully have a better understanding of the amount of rock that you may need for your aquarium. Make sure to read Reef Tank Resource’s Aqua Scaping article for more ideas on designing your new aquarium.

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