First let me nearly disqualify myself as I do not have a dirt tank. My 60g is a somewhat sterile canvas with a gravel/sand substrate and (dare I say it) plastic plants (although I do have real rocks!).

I have however been involved in organic gardening for over 30 years. In so doing, I have made tons of compost and have even made truckloads of vermicompost (composting with redworms).

In order to produce healthy plants, fruits and vegetables, you have to FEED THE SOIL. There is an incredible ecology that happens in the soil in order to breakdown organic matter into plant usable nutrients. 

So your starting out with nutrient rich organic potting soil, perhaps augmented by some clay and/or other additives. After a bunch of water changes and filtration and a bunch of plants, things are looking good. Assuming decent lighting and water quality, the plants should be growing really well...but unless you take measures, things will level off and in time, plants will not grow so well. Now here's where some will be tempted to start using petro-chemical fertilizers in liquid or root tab forms. Well, if you were gonna end up doint that, you might as well not started with dirt at all - just used sand/gravel and done hydroponics!

If you have a dirt tank, you need to FEED THE SOIL and develop the ecosystem. In so doing, we'll borrow a couple of ideas from the 'deep sand bed' folks.

First, your soil needs a constant supply of organic matter so to decay and feed your soil. So put that gravel siphon down and leave the mulm alone. A layer of decaying mulm is essential in maintaining the health of your aquatic soil. If you want a cleaner look, say in front, slosh the mulm towards the more heavily planted rear of the tank rather than removing it. Of course you can do some cleanup, but try to keep as much organic waste as possible that will feed your subsoil...and ultimately feed your plants.

If you don't have sufficient stock, you still need to find a way to organically enrich the soil - perhaps by adding fish food for invisible fish ;-)

Consider adding some subsoil life. California black worms are the aquatic equivalent to redworms. They will burrow and aerate the soil, process decaying organic matter and their castings are pure organic gold in the substrate.They will also make a most excellent supplemental food source for your fish.

Malaysian Trumpet Snails will burrow in the top inch of gravel/sand keeping it aerated. This assists the bacteria that lives there and breaks down organic matter further.

I could go on and on here, but don't want to 'preach to the choir' or wear out my welcome. I'm very interested in the soil substrate aquarium and will start one when I have the space and time. I wrote this because I've learned alot about good growing soils and what I've seen so far regarding the 'dirt tank' doesn't seem to address long term organic maintenance of the subsoil, so I thought I'd toss this out as food for thought.

If you got this far, thanks for reading - hope you saw some value in it.

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