On Dirted Tanks

This is part three of a series on aquaria. Click here to go to the first article. Click here to see all articles.

    Dirted aquaria are a mythical thing in the hobby, relegated to those who are brave. The group in the dirted aquaria are the most die-hard of all aquarium hobbyists. Building a dirted aquarium might be the closest thing to having a slice of a river or lake we can get in the hobby. A dirted aquarium will have a layer of dirt, with gravel and sand with live plants converting those nutrients in the dirt into mass growth.

There are a lot of aquasoils out there which can give your aquatic plants the nutrients they need to create massive growth. The downside to them is they are quite expensive. I got a bag of ADA Amazonia v2 and it was more expensive than the 50lbs of pool filter sand I bought for the tank, and has been used in 3 other tanks. There is a better alternative out there, and it’s closer than you think.

1. What are the benefits?

    According to Diana Walstad in her book on the subject Ecology of the Planted Aquarium: A practical manual and Scientific Treatise for the Home Aquarist, the dirt gives a good media for plants to grow in, better than gravel or sand alone. You will need to fertilize less (if at all), toxic bacteria prevention, and need little maintenance. The dirt below your substrate is there to help your plants and critters have a more natural life and need less maintenance, which means you get to spend more time enjoying the tank instead of working on it. Further, you will need to spend less money on your tank because you’ve created a living ecosystem as opposed to a tightly controlled display.

The dirt outside your home is loaded with all the things your plants need in it. Beneficial bacteria, fungi, nutrients, and minerals; the best part is it’s free. The better you care for your soil as a gardener, the better the soil will be for your tank. All you need to do is cap the dirt with some sand or gravel and boom, instant awesome substrate.

To show how natural this is, let me tell you about what I found when I changed the substrate in my 35 gallon aquarium to do the dirted method. I found dirt mixed in with the gravel. You might have heard of this as mulm, but in essence, it is dirt made by your aquatic fungus turning waste into soil for your plants to feed off of. My gravel substrate was loaded with this dirt and my plants were doing well, but nothing like they are now.

Adding dirt has further benefits of being the single best home for your beneficial bacteria to live. Dirt has the highest value of any substrate for housing beneficial bacteria. Further, the fungus that your plants need to live, will thrive much better with soil than with gravel as that is what they have evolved to live in. Beyond all that, all fortified soils (including dirt) run out of nutrients eventually, usually after a couple of years. I feel paying nothing for something I will need to reset every few years than a hundred dollars or more for my 35 gallon, or more for our larger tanks.

Detractors to the dirted tank method bring up the toxic buildup of gasses under the surface which can burst and kill your fish. First, the gas bubbles should never build up enough to be dangerous, it should dissipate without consequence and your plant roots will take care of most of the toxins. Second, if you are worried about it, you can take your planting tweezers to stab into the substrate to allow the gas to escape. The bubbles will be somewhat frequent in the first couple of weeks to month, but almost 6 months later, I don’t see any bubbles coming up any more.

What about gravel vacuuming you ask? I wouldn’t recommend disturbing your substrate in any tank with plants. In a dirted tank you will end up pulling the dirt up above your capping substrate. Further any waste will work its way down into the dirt eventually where it will become fertilizer for your plants. Further, plants can stretch their roots out up to six inches from the center so shoving a tube into the substrate can damage the roots and take nutrients away from your plants. 

How to set up a dirted tank.

    Setting up a dirted tank is not much different than setting up a normal aquarium substrate, just you are adding dirt. Follow along with my pictures below to see how I converted my standard aquarium into a dirted tank.

Step one:

    Pull the plants and get all the livestock out. This can be easier said than done if you have a well-established tank like I did. This tank had been running for about a year when I did this so there was quite a bit of mulm down in the substrate which when I pulled the plants up made the water murky and hard to see the fish in. The plants went into a bucket and my 8 corys, 3 harlequin rasboras, 4 ottos, and a large number of cherry and ghost shrimp went into another tank. 

Step two:

    Removing the substrate was probably one of the easier parts of this job. I scooped it out with my hands, as well as help from my fiancee, and put it in buckets. The tank was then taken outside and we strained the last of the sludge through a net to try to save as many shrimp as possible. I’m not kidding, there were tons of mud-blood cherry shrimp in there. I hosed out the tank and used a scrubber to clean off the excess algae on the walls. When I brought the tank inside, I began the reconstruction.

Step three:

    Once the tank was inside, I laid down a hump of the old gravel substrate to help build up the back to make a more dynamic slope for my plants (that didn’t work out in the end. I went into the back yard and got some dirt and filled a two gallon bucket. I dropped the dirt in and levelled out the slope.  I then put a bag of ADA Amazonia 2 on top of the dirt and sprinkled the Amazonia tabs randomly. I then coated it all with a layer of pool filter sand. 

Step four:

    The careful refilling of the tank then began. I put a saucer down so as not to disturb the sand scape I had created. Once it was about half way filled, I put my filters and heater in and then the wood went in. My girlfriend then replanted (as that’s her thing) all my plants. Once all the plants went back in we filled it back up all the way and started my filters up.

Since doing the dirt bottom in my tank, my need for maintenance has plummeted. I don’t need to do weekly water changes, I take a bit off to water my orchids and maybe do a normal change once per month. My tank is much more an ecosystem now instead of a water box that I have to keep running with near constant input.