Drainage Layer - A layer of the substrate to allow excess water to collect and drain away from the soil. To help preserve the soil and not create a swamp or bog condition that would encourage bacteria growth (and not the good kind). The drainage layer needs to be a minimum of 1.5" deep, but it is more typical to see them 2 - 3" deep

The drainage layer consists of 3 basic parts.

1 - Drainage material - You can use a variety of materials. Aquarium gravel, river rocks, Leca (expanded clay), or Light wieght drainage material (sold by hobby supply sites like Josh's Frogs or NeHerp). This material will need to be put in to be 2 - 3" deep.

2 - A material to stop soil from falling down into the drainage layer. You can use anything that is non toxic and will not break down fast. You also want it to allow air and water to pass through easily but not soil. You can use typical weed block or Fiberglass window screen. This will be laid over the top of the drainage material. Let it go up the sides of the tank about an inch so it creates a sort of bowl to hold the soil mixture.

Optional - You can get some quilt batting and use it between the drainage material and screen to add additional filtration to catch any tiny soil particles. This can be cut exactly to size and does not need to go up the sides of the tank.

3. A way to siphon off excess water. As time progresses the drainage layer will accumulate water and will need to be drained as it gets closer to the soil. Typically a piece of PVC pipe is hidden in the corner of a back ground and goes down into the drainage layer (a sponge or typical aquarium filter) can be places at the bottom to keep from clogging the siphon tube. Then when needed you can stick the siphone hose down the PVC and drain off excess water. You want to keep the drainage layer about 1/2 to 3/4 full of water. Any micro fauna you add to the soil will go down to the water or near it to breed.