Should I cap the aquasoil with sand?Updated a month ago

You can cover the Aquasoil for aesthetic reasons, but plants root best in pure Aquasoil. Plant roots work by contact with the soil and any additional layer of separation that reduces root to substrate contact will reduce the effectiveness of the soil layer. This will affect smaller plants the most, while larger plants with deeper roots can easily overcome a sand/gravel cap.

Thin caps (1 to 1.5 inches) will not significantly prevent nutrient leaching due to the porous nature of sand/gravel caps. There will still be significant water movement across the boundary. Thicker caps (2.5 inches and above) can prevent water movement and have some effect, but plant roots will find it more difficult to find the soil layer when planting. This will affect smaller plants more than larger ones.

We do not cover aquasoil in any of the 2hr Aquarist gallery tanks except for aesthetic reasons. In the tank below, Aquasoil is used in the middle and back under coarse sand.