Soil Substrates 101
This topic will explain how to set up a soil-substrate aquarium, and the risks/benefits of doing so. I will be updating this as I create one of my 10 gallon aquariums. If you have an empty aquarium, you can do the steps as I do them, over the course of a month or so.
Benefits of a Soil Substrate NPT (Natural Planted Tank)
Good plant growth.
No injected CO2 required.
No or little algae.
No need for additional fertilisers. (and less overall cost)
No need for frequent water changes once the tank is established. (Many people change the water every 6 months, some people less often)
Biofilter is not be required (plants will take care of the ammonia, nitrite and nitrate, and the soil bacteria will also consume nitrogen. Water movement is suggested but not required.)
Slightly more flexibility in the lighting intensity.
Organisms in the soil (planaria, etc) will usually thrive (usually hard to spot unless you look for them), and provide food for any fry present.
Risks of a Soil Substrate NPT
Some soils are nutrient rich and can release ammonia or chlorine into the aquarium for a long period of time.
Prevented by: Mineralising topsoil and only using acceptable bagged soils.
The soil layer can become anaerobic, which is a very very bad thing. Anaerobic basically means that the soil isn't oxygenated enough, and the bad bacteria takes over. Bubbles rising from the substrate and a strong sulfur/rotten egg smell is a dead giveaway.
Prevented by: Using 2 inches or less of soil mixture, and 1.5 inches or less of gravel. If using sand, use 1 inch or less. MTS (trumpet snails), Blackworms (Also sold as 'California Blackworms'- actually Lumbriculus variegatus), or poking the substrate frequently the first few weeks can also help prevent anaerobic conditions.
It is also important to stock with plants that have extensive root systems- plant roots have the ability to prevent anaerobic conditions.
Some good rooted plants are:
Echinodorus species (Make sure you find species that are proper for your tank)
Vallisneria (For taller aquariums)
Even safe soils can leach ammonia into the water faster than the plants can assimilate it, causing algae outbreaks or toxic ammonia levels the first weeks or months.
Prevented by: Initially stocking the aquarium with fast-growing plants, floating plants (Water lettuce, frogbit, some stem plants left floating) to use nutrients. Also make sure you have sufficient light.
Good fast growing plants should be used when you start up the aquarium. Slower-growing plants can be added later.
Stem plants in these families are all fast growing- Rotala sp. Ludwigea sp. Egeria sp. Hygrophila sp.- along with rooted plants listed above. 'Mineralising' the soil also will eliminate raw organics and give them a chance to break down before you set the aquarium up.
Many of these risks can also be prevented by using the Dry Start Method, but that's an entirely different process which I've never tried. The basic concept is to set up the aquarium as a terrarium, with 'bog plants'. The plants will grow much faster in their emersed state, and when the aquarium has grown in you fill it up with water. If there is interest, I may set up one of my 10s using that process and record it in a different topic.
I use a combination of 'mineralised' garden soil (dug out of my yard) and "miracle grow organic choice" potting soil. If you are wary of using soil from your yard, you can buy cheap "top soil" from a home improvement store.
As I said, I will be posting these steps as I do them, and try to take photos regularly to show the growth (along with any pitfalls) that it experiances. It will be a South American regional biotope stocked with livebearers. (Yes, I'm converting my 10G livebearer :-D)
STEP ONE: Mineralising the soil
This is straight-forward, so no pictures yet.
I have an area in my back yard that frequently floods, so I will be using soil from that area. The fact that it floods is a dead giveaway that it is rich in clay. Clay is nutrient-rich, but has an extremely high CEC (Cation exchange capacity) which basically means it releases it's nutrients very slowly, and directly to the plant's roots. You can use any soil that is free from chemical fertilisers, pesticides, etc.
Since I use a 1:2 mixture of mineralised soil and "Organic Choice potting soil", you don't need much topsoil. I only use about a cupful for every 5 gallons. No need to measure it now, just "aquire" about a shovel-load for every ten gallons. Any soil left can go back where it came from or stored for later use.
Many people use a tarp and water it with the hose, but I have a wide 4-5 gallon bucket that I use. Break up the soil, and remove any large rocks, roots, grass and organic matter. (If you miss some, that's okay, it will float later if you are using a bucket.)
If you are using a tarp, spread it out to approximately 1 inch thick, and spray it with the hose (just so it is damp, not soggy). If you are using a bucket, I break it up into small pieces and fill the container so the soil is almost covered.
When the soil is dry, wet it again. If you are using a bucket, then stir it so the organic material floats to the top, pour off half the water, refill, and wait.
While this is working, you can make sure your tank is clean and start researching and deciding which plants and fish you will want.