How Much Live Rock Do You Really Need?

The amount of live rock needed in your aquarium is based on several factors

The amount of live rock needed in your aquarium is based on several factors

Once hobby newcomers learn what live rock is and all the benefits it can provide in marine aquariums, the next big question they invariably ask is, “How much of it do I need for my tank?” More experienced fellow hobbyists, eager to be of help, typically respond with a pat answer along the lines of “somewhere between one and one-and-a-half pounds per gallon.”

While this type of formula is certainly convenient and eliminates guesswork, it unfortunately fails to address several key factors that must be considered when determining how much rock is actually appropriate for a given system. Here are just a few of them:

Differing density

Pound for pound, not all live rock stacks up the same. The density of live rock can vary considerably from one type/collection locale to another—and a highly porous rock is going to be significantly lighter than a very dense rock of the same size. (Visualize holding a chunk of lava rock in one hand and an identically sized chunk of granite in the other, and you’ll have the idea.) So, you can expect 100 pounds of highly porous rock to take up a lot more space in your tank than 100 pounds of dense rock will.

Livestock objectives

How much rock you’ll want to place in your tank will also vary based on your objectives for the system. For example, a full-blown reef tank might require more rock than a fish-only system to ensure there’s an adequate foundation for the various invertebrates you plan to keep. On the other hand, if your objective is a fish-only system and you plan to use live rock primarily for biofiltration, you can probably get by with less.

You also have to consider the unique needs of the different species you’ll be housing. Will the fish need a lot of open swimming space, or will they be better off with lots of nooks and crannies for hiding? Will any of them be burrowers that need an open plot of substrate? Will your invertebrate population include any corals that are best placed down on a sandy substrate rather than up on the rocks, such as Fungia, Catalaphyllia, or Trachyphyllia? In general, will you stock your tank lightly, heavily, or somewhere in between? All of these factors will have at least some bearing on how much live rock is appropriate for your tank.

Skimming and water-change regimen

Of course, if you do a really good job of removing dissolved organic compounds from your system before they have a chance to decompose and contribute to the bioload—via vigorous protein skimming, regular partial water changes, etc.—you may not need as much live rock for biofiltration purposes.

Potential use of non-live rock

Aquascaping does not have to be achieved entirely with expensive live rock. Many hobbyists choose to use base rock as a foundation for their rockwork and then top it with choice pieces of live rock in an effort to contain costs.

What am I forgetting?
As always, I’m sure I’ve overlooked some important points here. So, fellow salties, if you can think of any other factors that influence how much live rock one should purchase, please share them in the comment section below.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Sound advice for reefers with no available – working – Biological Filtrattion: no doubt ! However everyone seems to have forgotten that Biological Filtration has been around for centuries… Marketing strategies and Technocratic Imperatives have pushed it aside to fill LFS shelves with New Age Wonders… What a pity. Old School Aquarists know that Ammonia destroys Undergravel Aerobic Bacteria but it can be dealt with in a natural fashion without costly hardware. Thus Undergravel Biological Filtration can be re-introduced into Marine Tanks for the benefit of those specimens that simply can’t make it in the long run in Sterile Tanks !! To discover this new approach simply have a look at the Orion Briefings on our website – – . And by the way discover the process of Large Symbiotic Anemone Reproduction in such tanks… You might realize that there are not ONE but several approaches to Marine Aquariophilia.
    Don’t forget that Live Rock Filtration is minimal in a Reef Tank: – It gets covered with a BioFilm much in the same way as charcoal in a canister filter that prevents water from circulating through it. Even if you blast a large basker or powerhead at it occasionaly… And Protein Skimming destroys everything that is good in Marine Salt Water which has Aquarists fumbling with additives of all sorts to replenish…. Great if you like chasing your tail like a puppy…
    The ONE GREAT THING about Live Rock is the vast Flora and Fauna that come with it: much of which is destroyed in a traditional reef tank: the good news is that this wealth of Marine Life will developp in a Marine Biological Filtration tank !!!
    Have a Great Day Jeff
    Sylvain at SBMarine – –

    • Jeff Kurtz says

      Hi Sylvain! It’s great to hear from you as always! Thanks for these insights, and we’ll be sure to check out the info you mention on your website.

      • How very generous of you Jeff…
        We take it as a an immense honor coming from a World Authority !! And also wish to thank the whole Saltwater Smarts team for their open minds and thorough coverage of all topics. And it comes straight from the heart….. 🙂
        I have personally learned a lot from your combined experience even though SBMarine is into Marine Biological Systems. There is an overlap of knowledge however that links both worlds. and it is ever so needed to all Aquarists. In fact both approaches complement each other in that Major Pitfalls exist in both. Sharing of knowledge becomes more relevant in this perspective.
        Take Care

        Sylvain at SBMarine ( )

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