It should come as no surprise that we’re big fans of natural aquariums. When people think of natural freshwater tanks, they usually think of plants first. However, there are other natural decor options for both freshwater and reef tanks that contribute beautifully to aqua-scapes, including rocks.

Not all rocks are suitable for aquariums, but many are just fine. I have a 90 gallon display tank in my livingroom that is done entirely in beach rock that I gathered myself. I also use a lot of Tufa Rock and Texas Holey Rock to help balance my pH/KH. While changes in pH are often a concern of those considering rocks for their freshwater aquarium, I have found that it takes a lot of rock to have a significant impact on water parameters. The rocks dissolve much too slowly to cause spikes or major fluctuations during water changes.

Rocks can serve practical purposes as well. Porous rocks are wonderful for beneficial bacteria colonies, and they’re perfect for plants that anchor their roots above the substrate, like Java Fern and Anubias. As mentioned, some rocks help boost the KH/pH for environmental stabilization. Stones can be used to create biotopes meant to replicate the wild environment. You can also use rocks to create nooks & caves for fish to hide in.

“An advantage of natural rock is that no two pieces are the same, so you can be confident of a unique look whichever you choose,” says Mark Cropper, aquarium expert at SwellUK. Seiryu rock looks spectacular in any freshwater aquarium. It is widely used by the aqua-scaping community, due to its stark, natural beauty and lack of effect on the tank. However, it can raise the pH slightly so keep an eye on levels. For a reef aquarium, live rock is a popular choice. A living organism, it provides biological filtration as millions of bacteria thrive on its porous surface. It creates a piece of breathing art in your tank.”

Rocks Commonly Used in Aquariums

  • Tufa Rock
  • Texas Holey Rock
  • Limestone / Dolomite – Will increase the KH & pH of your water. That could be a good thing if you have baby-soft water like mine or if you want to keep fish like African Cichlids. It’s great for aquatic snail shells too.
  • Dragon stone
  • Granite
  • Seiryu stone – Slightly raises pH.
  • Volcanic or Lava Rock
  • Petrified Wood
  • Pagoda stone
  • Elephant Skin Rock
  • Quartz, Crystalline Quartz and Microcrystalline Quartz
  • Onyx
  • Slate
  • Sandstone – May increase your pH.
Glossolepis pseudoincisus Rainbowfish
A young Glossolepis pseudoincisus Rainbowfish with Tufa Rock and other stones in our aquarium.

Notes of Caution: 

  • Check rocks for sharp edges to avoid injury.
  • It’s often a good rule of thumb to avoid rocks with red veins as that usually indicates iron or copper (unless you know otherwise).
  • You should also avoid “Fool’s Gold” (iron pyrite).
  • If you’re concerned about increasing pH, you can test for calcite, dolomite and siderite by pouring vinegar or diluted hydrochloric acid over the rock. If it bubbles, it could potentially raise the pH.
  • Clean rocks with a scrub brush (no soap) before putting them in your fish tank. For disinfection, pour boiling water over them and allow to cool before touching. Never bake, microwave, or boil the rocks themselves as they may explode, causing serious damage or injury.

??? What is your favorite aquarium rock? Please share in the comments below.

You may also be interested in reading:
6 Fast-Growing Plants for Natural Cleaning in Standard Aquariums
DIY Natural Fertilizer Balls for Aquarium Plants (Infographic)
Increase or Decrease Freshwater Aquarium pH Naturally


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5 thoughts on “Natural Rocks for Aquarium Decor ©

  1. I love working with rock in aquariums! Plants are nice but they take so much work. You can do a gorgeous rockscape and it stays lovely.

  2. Thanks for turning me onto Swellpets! Great selection and I love the stones. I’ll have to check if shipping them would be worthwhile but I think I could swing one or two. 😉

  3. Texas holey rock is my fave! I don’t think it increased my pH because it was high anyway, but it might bump up acidic water. Thanks for the great fish posts.

  4. I never put much thought about the rocks that I put into my aquarium. Although I did change them out a few months ago to something more natural. I let my 10 year old daughter choose some hot pink gravel and then realized that probably wasn’t a good idea. I switched over to what I think may be quartz. They are very smooth rocks that remind me of the ones we find in our local lake.

  5. Sometimes its hard to see them fizz but even if it’s only a little it can up the ph. It’s more pronounced in small tanks but you’re right it does take quite a bit. Smaller pieces or sand can really make it hop up especially if you have lots of water moving. Great article!

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