On this page you learn what rocks are safe for your aquarium and how to test them.

There are two very simple ways to test rock to be sure they are safe for your aquarium. The first method uses Muriatic Acid (MA). This can be found at either a swimming pool supply store or possibly a hydroponic supply store. To test any given rock, put a few drops of MA on the rock, wait a couple of seconds and watch for bubbles. If bubbles are seen, this rock is NOT safe. Distilled white vinegar can also be used in a pinch. The MA test is more accurate though.

One point to remember is some rocks are made up of a conglomerate of differing minerals and smaller rocks. It would be a good idea to test each rock in numerous places. This test can also be used to verify you choice of substrate for compatibility.

Below is a list of rocks that are safe for aquarium use.

Safe Rocks:

• Crystalline Quartz
• (Rock Crystal, Amethyst, Citrine, Rose Quartz, Smokey Quartz)
• Granite
• Jade
• Lava Rock
• Microcrystalline Quartz
  (Jasper, Agate, Chalcedony, Sard, Carnelian)
• Onyx
• Petrified Wood
• Quartz
• Slate

Unsafe Rocks:

• Coal
  (Commercially harvested coal is treated with an oil by-product to reduce dust)
• Coral
• Dolomite
• Fools Gold
  (or any other rock with metallic veins--Acid Producing)
• Fossils
• Limestone
• Marble
• Sandstone

Keep in mind that some of these rocks can be used in some tanks. Crushed Coral makes an excellent substrate for maintaining water quality for African Cichlids. You can even use some rocks that come from limestone to do the same. Limestone will usually do nothing more than raise your water parameters. If you decide to use rocks that will contribute to the overall hardness, make sure you test the water parameters to get a handle on just how high your levels will increase over time.