Seachem Onyx Sand 7.7 lb Planted Aquarium Substrate
Seachem Onyx Sand is a premium dark gray to black sand substrate designed for freshwater planted aquariums and aquariums with species that prefer higher pH and hardness. Its natural dark coloration creates a bold aquascape look while helping plants, fish, shrimp, rocks, and driftwood stand out beautifully.
Onyx Sand is porous, long-lasting, and carbonate-rich, making it a strong choice for planted tanks, hard water aquariums, African cichlid setups, livebearer tanks, and aquascaped freshwater displays. Because it may raise pH and hardness, it is especially useful for aquariums where a more alkaline environment is desired.
Key Features
- Great for Planted Aquariums: Porous sand substrate provides a stable base for rooted aquatic plants.
- Carbonate-Rich Formula: May help buffer pH and hardness for species that prefer alkaline water.
- Natural Dark Color: Dark gray to black tones create strong contrast with plants, fish, shrimp, and decor.
- Long-Lasting Substrate: Does not break down or require routine replacement over time.
- Hard Water Friendly: Useful for planted aquariums, African cichlids, livebearers, and other harder-water setups.
- Use Alone or Mixed: Can be used as the main substrate or blended with other aquarium sands and gravels.
- 7.7 lb Bag: Convenient size for nano tanks, small aquariums, accent areas, or deeper planting zones.
Product Details
- Brand: Seachem
- Product: Onyx Sand
- Size: 7.7 lb bag
- Type: Porous planted aquarium sand substrate
- Color: Dark gray to black
- Water Chemistry: Carbonate-rich; may raise pH and hardness
- Best For: Planted tanks, hard water aquariums, African cichlids, livebearers, aquascapes, and root-feeding plants
Best For
- Freshwater planted aquariums
- Hard water aquarium setups
- African cichlid aquariums
- Livebearer tanks
- Root-feeding aquarium plants
- Dark substrate aquascapes
- Community aquariums with compatible water needs
- Accent areas or deeper planting zones
Plant Benefits
Seachem Onyx Sand provides a stable porous substrate base for rooted aquarium plants. Its fine texture helps plants anchor while creating a clean, natural-looking substrate bed.
For demanding plants or heavy root feeders, Onyx Sand works best when paired with root tabs, liquid fertilizers, proper lighting, and regular aquarium maintenance.
Water Chemistry Note
Unlike neutral substrates, Seachem Onyx Sand is carbonate-rich and may slightly increase aquarium pH and hardness. This makes it a good option for planted tanks and freshwater species that prefer harder, more alkaline water.
For soft-water fish or shrimp that require lower pH and very soft water, test your water regularly and confirm that Onyx Sand fits the needs of your livestock.
Usage Tips
- Rinse well before use to help remove dust and fine particles.
- Add water slowly over a plate, bowl, or plastic bag to avoid disturbing the substrate.
- Use a deeper layer in areas where heavy planting is planned.
- Pair with root tabs or liquid fertilizers for nutrient-demanding plants.
- Test pH and hardness after setup, especially when keeping sensitive fish or shrimp.
Coverage Guide
Coverage will vary based on tank dimensions, desired substrate depth, and aquascaping style. One 7.7 lb bag is commonly used for nano aquariums, small planted tanks, accent sections, or deeper planting zones in larger aquascapes.
For larger aquariums or deeper substrate beds, multiple bags may be needed.
Why Choose Seachem Onyx Sand?
Seachem Onyx Sand is a strong choice for aquarists who want a dark planted tank substrate that also supports harder-water aquarium setups. Its dark color adds contrast, while its carbonate-rich composition can help maintain conditions preferred by certain plants and freshwater species.
It is especially useful for aquascapes with plants, rocks, African cichlids, livebearers, and other freshwater aquarium layouts where a slightly higher pH and hardness are desired.
Frequently Asked Questions
Will Seachem Onyx Sand raise pH?
Yes. Onyx Sand is carbonate-rich and may slightly increase pH and hardness, making it a good choice for plants and freshwater species that prefer more alkaline conditions.
Do I need to rinse Onyx Sand before use?
Yes. Rinse well before adding it to the aquarium to help remove dust and reduce initial cloudiness.
Can Seachem Onyx Sand be used with bottom-dwelling fish?
Yes. The fine grain is suitable for many bottom-dwelling freshwater fish when rinsed and used properly. Always match the substrate and water parameters to the needs of the species being kept.
Is Onyx Sand safe for shrimp tanks?
Yes, but it may buffer pH and hardness higher than neutral. It is best for shrimp species that tolerate or prefer harder, more alkaline water.
Can Onyx Sand be used in planted aquariums?
Yes. Onyx Sand is designed for planted aquariums and provides a stable base for rooted plants. Root tabs may be helpful for heavy root-feeding plants.
Does Onyx Sand need to be replaced?
No. Onyx Sand is long-lasting and does not break down or require routine replacement.
Available at Tropical Treasures Wyo
Shop Seachem Onyx Sand 7.7 lb Planted Aquarium Substrate online or in-store at Tropical Treasures Wyo in Cheyenne, Wyoming. This dark carbonate-rich aquarium substrate is a great choice for planted tanks, hard water aquariums, African cichlid setups, livebearer tanks, and natural freshwater aquascapes.
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