# fish stock density



## Durian (Feb 19, 2008)

I am interested in increasing the density of fish in a natural tank. The "conventional" wisdom for tank of soil+gravel+plants, with circulation but no filter, is only about 1/3 the fish density of the more labor-intensive gravel/filter/plastic-plant approaches. However I came across the beautiful and inspiring website of Todd Crail, http://www.farmertodd.com/ , who published an article "System Design for the Ultimate Native Fish Aquarium", American Currents vol.32 no.2, pp 13-19 (2006), describing how he achieves a *much* higher fish density [incidentally this is where I first leaned of Diana Walstad's book Ecology of the Planted Aquarium]. He uses a very deep sand bed, heavy planting, strong circulation, lots of bottom feeders, and heavy feeding. The result is a very healthy low-maintenance tank with no need for water changes or gravel cleaning. He argues that biological activity in the deep sand is the key, but I wonder if the strong circulation or the bottom feeders and heavy feeding also play an important role? What's the science, and how does this jibe with what's written in "Ecology of the Planted Aquarium" about wet/dry filters being counterproductive because of competition between bacteria and plants for ammonia?

Thanks, -Doug


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## ItsDubC (Jan 12, 2008)

Wouldn't the deep sand create a lot of anaerobic pockets in the substrate? I don't know how much if any of an effect the increased water circulation would have on deeper portions of the substrate.

As far as my understanding goes, heavy planting is the key to balancing a filter-less tank. Mrs. Walstad advocates heavy planting just as much as this gentleman it seems. However, plants need nutrients that I don't think a sand-only substrate can provide for very long. This is why Mrs. Walstad recommends the use of soil.


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## lauraleellbp (Jan 31, 2008)

Sounds kind of like he was trying to create an in-tank refugium. Did he mention if the tank was stocked with anything to intentionally live in the deep sand bed?

What did he have to say about algae?


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## dwalstad (Apr 14, 2006)

Without soil, I don't think you can get plants to grow well enough to accommodate a high fish density. If this fellow's aquarium was well-established, fish mulm from heavy feeding might have accumulated enough mulm to get some plant growth and allow for a fair number of fish. However, sand is truly a poor planting medium, and you could end up with a tank full of dead, rotting plants and highly stressed fish. 

The key to a high density of fish is a soil underlayer, intense light, a tank with lots of surface area (promotes oxygenation), and a nice combination of emergent/submerged plants. Kind of like what the pond folk do.

Fig 3 in my book shows a 20 gal long tank packed with plants and fish. At times I'm sure I had at least 100 juvenile cichlids of 1" size in this tank, and they did great.


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## mistergreen (Mar 3, 2007)

I'm not a big fan of overstocking on fish. It doesn't help the plants out and definitely not the fish. The excess NH4 will just trigger algae blooms and cause stress and death for the fish...


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## Durian (Feb 19, 2008)

Thank you for all the responses! I should have mentioned that Todd Craig's article at http://www.farmertodd.com/pdfs/native_fish_tank.pdf describes two different substrates -- sand mixed with flourite, and topsoil and river mud covered with sand/gravel. He's quite adamant that a deep substrate is key. That's what I'm trying to understand -- in scientific terms could there be an unrecognized benefit to having very deep substrate.


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## BryceM (Nov 6, 2005)

The whole deep substrate issue is an interesting one. In theory it has both potential benefits and potential problems. Reefers are routinely using a deep sand bed to intentionally create an anaerobic zone.

In our side of the hobby, most people regard an anaerobic zone as undesirable. It could actually be quite useful in keeping waste concentrations low. Nitrates, for one, can be converted to back to atmospheric N2. Ammonia/ammonium is the usual issue with a heavily overstocked tank and removal of nitrogen back to its elemental form would help keep the regular nitrogen cycle moving forward. Adding plants and trying to meet their needs simultaneously can be tricky. 

Production of H2S (rotten egg gas) can be an issue though. As long as an anaerobic zone stays undisturbed, there is usually no problem. Once you inadvertently pull up a plant, stir the deep substrate, or release the H2S gas, chaos can ensue almost instantly.

I gave a deep substrate bed an accidental stir once and watched a dozen of my favorite fish die right before my eyes. It literally killed them within seconds.


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## lauraleellbp (Jan 31, 2008)

Exactly. Avoiding hydrogen sulfide would be the big problem with a deep substrate, and I'm at a loss as to desirable FW organisms that would keep the substrate oxygenated?


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## newbie314 (Mar 2, 2007)

But if you have the biolayers that consume the Sulfates should be a problem.
Also emergent plants with roots can help aerate the soil.


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