Can I put sand on top of aquarium soil?

Yes, you can put sand on top of aquarium soil. This is often referred to as "capping" the soil, and it's a common practice in planted aquariums.

Why Cap Aquarium Soil with Sand?

Capping aquarium soil with sand offers several benefits:

Reduces Mess: Aquarium soil can be messy and cloud the water, especially when first introduced or disturbed. A sand cap helps contain the soil and prevent it from dispersing into the water column.
Minimizes Leaching: Aquarium soils, particularly those rich in nutrients, can leach ammonia and other organics into the water. A sand cap acts as a barrier, reducing the amount of leaching and helping to maintain water quality.
Creates a Stable Substrate: The sand layer provides a more stable surface for planting and prevents roots from directly contacting the nutrient-rich soil. This helps prevent uprooting.

Here's a simple guide on how to cap your aquarium soil with sand:

Choose the Right Sand: Opt for inert sand specifically designed for aquariums. Play sand or construction sand is not recommended as it may contain contaminants or alter water parameters. Pool filter sand is a common and cost-effective option.
Prepare the Soil Layer: Add the aquarium soil to the tank, ensuring it's evenly distributed and at the desired depth.
Add the Sand Cap: Gently pour the sand over the soil layer. Aim for a sand cap thickness of 1-2 inches (2.5-5 cm). This is generally sufficient to contain the soil and prevent leaching.
Fill the Tank Carefully: When filling the aquarium with water, place a dish or bag on top of the substrate to prevent disturbing the sand and soil layers.

Sand Type: The type of sand you use matters. Fine sand can compact over time, potentially creating anaerobic pockets. A slightly coarser sand is generally preferred.
Maintenance: Regular gravel vacuuming is important to prevent the buildup of debris and maintain water quality. Be careful not to disturb the sand layer too much while vacuuming.

Capping aquarium soil with sand can be a beneficial technique for creating a healthy and stable planted aquarium environment.