# The Genius of D. Walstad



## Jarrod987 (Aug 18, 2015)

I have been listening to Phil Edwards talk at the 2015 AGA Conference regarding substrates in the Aquarium. Diana Walstad was there and talked with him Briefly.

Some of the things that were said was that the soil or any other substrate needed to right particle size to be good for plants. Not too big or too small. If too small the roots would not be able to get enough oxygen out into the substrate and keep it aerobic. Once it goes anaerobic the plants suffers and eventually dies.

Substrates like Sand and Gravel are inert and are said to be "Durable" and can last for a very long time. The soil is said to break down after a few years. The time varies by tank but when it does it needs to be replaced to keep the plants growing.

There was talk of the various things that happen to Iron and Nitrogen in the Aerobic and anaerobic zones. The plant roots stay in the aerobic zone. In fact they make it the aerobic zone. 

Some of the chemicals produced in the anaerobic zone are toxic. That is why soil can be a problem when used by itself etc. It eventually becomes a muddy mess as the clay breaks down or goes impacted and anaerobic. It was said that using critters to aerate the soil does work great on land because they make small tunnels full of air which has oxygen in it etc. However, Under water it does not work because our substrates just collapse behind the critter and the water has 10% of the oxygen that air does above the soil. Under it, it would have none except the plant roots add it. It supports the bacteria in this way.

Now for DW's Genius. The Anaerobic layer does do some cool things for the plant I won't get into. The toxic gases such as Hydrogen Sulfide that it makes only go up as far as the aerobic layer above and that aerobic bacteria converts them to a safe form and also the plants can take them up. So what DW did was put a 1-1.5 inch layer of sand or gravel above the 1-1.5 inches of soil. This means the soil can go aerobic and stay that way. The plant roots should stay in the sand/gravel. I buried mine in the dirt because I did not know better but my plants seem OK. This inert aerobic layer should be durable and last 30-40 years. DW does say in her book she has tanks that have been running 20 years. She does feed heavy and also does remove the mulm when it gets 1/4 inch thick. She does not do Water changes or inject CO2 and she uses Low light.


----------



## Kai Witte (Jan 30, 2006)

Hello Jarrod,



> Some of the things that were said was that the soil or any other substrate needed to right particle size to be good for plants. Not too big or too small. If too small the roots would not be able to get enough oxygen out into the substrate and keep it aerobic. Once it goes anaerobic the plants suffers and eventually dies.
> 
> Substrates like Sand and Gravel are inert and are said to be "Durable" and can last for a very long time. The soil is said to break down after a few years. The time varies by tank but when it does it needs to be replaced to keep the plants growing.
> 
> ...


Just to state the obvious: It's a bit more complicated... 

Terrestial soils are complex habitats that can be seen as ecosystems in and off themselves. Aquatic soil usually has several layers (not just aerobic vs. anaerobic) complete with different, specialized critters/bacteria while strongly influencing each other.

Many aquatic plants do send their roots into anaerobic zones (and thrive by bringing oxygen in there as already stated); some also directly utilize carbon dioxide from the soil for photosynthesis by bringing it from the roots to the leaves.

However, not all plants are created equal and some have very specific requirements (usually those restricted to specialised niches/habitats): E. g. some of the specialised rheophytes won't send their roots into anaerobic soil.

BTW, clay won't break down in a lifetime unless under highly acidic conditions (not covered by Diana's method). Particle size also doesn't matter as much for plant roots in aquaria if you adapt the set-up accordingly.



> Now for DW's Genius. The Anaerobic layer does do some cool things for the plant I won't get into. The toxic gases such as Hydrogen Sulfide that it makes only go up as far as the aerobic layer above and that aerobic bacteria converts them to a safe form and also the plants can take them up. So what DW did was put a 1-1.5 inch layer of sand or gravel above the 1-1.5 inches of soil. This means the soil can go aerobic and stay that way. The plant roots should stay in the sand/gravel. I buried mine in the dirt because I did not know better but my plants seem OK. This inert aerobic layer should be durable and last 30-40 years. DW does say in her book she has tanks that have been running 20 years. She does feed heavy and also does remove the mulm when it gets 1/4 inch thick. She does not do Water changes or inject CO2 and she uses Low light.


I'm quite fond of Diana's book/method and appreciate that she spread the word, especially in the US and some other countries where planted aquaria were not common. I may quibble with the moniker genius: like many others before her, she read the science and came up with some good ideas/suggestions; none are exactly new though (topsoil and low-tech approaches have been used in aquaria for over one and a half century in ol' Europe...  )

There will always be lazy folks hoping for nature to do her job vs. control freaks, low tech vs. high tech approaches, preferences for gardening vs. habitat imitation, low budget vs. unlimited resources, etc. (with most people finding themselves somewhere in the multidimensional space between these extremes).

If you wish to adapt general recipes to your personal tastes (or rather those of the organisms inhabiting your tanks), do read the pertinent science papers and try to develop and test ideas, preferably by small changes first. If I recall correctly, there is an excellent reading list in Diana's book. Maybe others can add suggestions for additional reading here?


----------

