Seachem Onyx African Cichlid Substrate – Carbonate-Rich Natural Gravel (7kg)

Seachem Onyx is a especially fracted, natural substrate ideal for African cichlid aquariums. It is rich in carbonates, providing a gentle buffering effect that helps maintain a stable, alkaline pH—perfect for species from Lake Tanganyika and Lake Victoria.

Unlike chemically coated substrates, Onyx is completely natural and safe for all freshwater and marine environments. Its porous structure supports beneficial bacteria colonization, while its dark coloration enhances the vibrant hues of cichlids. Onyx can be used as a standalone substrate or blended with other gravels or sands such as Onyx Sand.

Key Features:

• Maintains pH in the 7.8–8.4 range
• Rich in calcium, magnesium, and carbonates
• Supports biological filtration and buffering
• Ideal for African cichlids and other alkaline water species
• pre-washed but may require rinsing before use

Product Specifications:

• Brand: Seachem
• Weight: 7 kg
• Form: Natural gravel (not sand)
• Color: Dark gray/black
• Country of Origin: United States

Mineral Composition (mg/kg):

• Calcium: 197,500
• Magnesium: 115,400
• Iron: 2,846
• Potassium: 417
• Aluminum, Cobalt, Chromium, Copper, Zinc – trace levels

Directions for Use:

Rinse before use to remove dust. Add to aquarium and fill slowly to avoid disturbing the substrate. Initial cloudiness is normal and will clear within 12 hours. Use Seachem Clarity to accelerate clearing if needed.