How to Make Synthetic Rocks for a Fish Tank

Most aquariums feature rocks to help mimic the natural habitats of the fish they contain. You can purchase manufactured rocks at a premium cost or you can use a bit of cement and manufacture your own. Cement is inexpensive, and will ultimately save you a lot of money. Making your own rocks also lets you express yourself creatively in the design of your aquarium̵7;s landscape.

Things You'll Need

  • Garden hose
  • Play sand
  • Portland cement
  • Cookie sheet
  • 5-Gallon bucket
  • Alkalinity testing strip
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Instructions

    • 1

      Wash the play sand that you'll use with the Portland cement with a garden hose.

    • 2

      Mix one part Portland cement with four parts play sand in a bucket. Unlike the cement you use to pour foundations, this mixture will feel more like clay or Play-Doh.

    • 3

      Ball the cement up with your hands; then place the cement onto a cookie sheet.

    • 4

      Form the cement into rocks with large holes in them for your fish to swim through. Or, form the cement to look like a cave so you can provide your fish with hiding places. The formation of the rock̵7;s design is up to you and how you want it to look in your aquarium. Allow at least 24 hours of drying time.

    • 5

      Place the rock in a bucket and then fill the bucket with water. If the fish you're housing prefer high alkalinity in the water, cure the rocks in water for three days. If they need low alkalinity, cure the rocks for three weeks. Check the water̵7;s alkalinity with a testing strip, which you can get from an aquarium supply retailer. Use the rock only when the water's alkalinity can be tolerated by your fish.