Originally Posted by firetyger
I really like the idea of low tech tanks...plants doing most of the filtering, fish doing most of the fertilizing, no CO2, low-medium lighting, etc. Yet I was wondering, will the number of fish ever get so great that keeping a planted tank low tech won't be an option anymore? For example, if you have 60 tetras in a 120 gallon tank, will you have to go high tech? Is the number fish so large that the equilibrium of the tank is hopelessly thrown off and using more equipment to balance things out will be necessary?
I also know the "one gallon per inch of fish" rule plays into this as well... So let's just say I'm puzzled about all this :) Any ideas?
You don't say just how "low-tech" you intend. Obviously there is a limit to any system at which point the fishload becomes greater than what the biological processes can handle and the system will crash. But that limit is variable depending upon several factors, as kald alluded to earlier.
The inch of fish to a gallon idea is usually unreliable and best forgotten because there are variables here as well. Not only the size of the mature fish--a 12-inch fish will not be healthy in 12 gallons of water; but their behaviours also factor into the equation. Fish that are lethargic require less space than those that are vigorous swimmers; this is less of a water quality issue as simply one of having sufficient room for the fish to "feel" comfortable. And a happy fish is a healthy fish because it is under no direct stress as a result of having inadequate space in which to "be itself."
Sixty tetras in a 120g tank is no where near the limit, provided the tank is well planted. And in this case, I am assuming no mechanical filter. Light is always required, although experienced aquarists have no difficulty maintaining planted aquaria with good daylight. But for most of us, myself included, artificial light is mandatory to ensure a regular and constant light of the necessary intensity and duration which is essential for good plant growth. Heat is dependant upon your location, but the majority of us have winters that are cool or cold and unless the fish room is itself maintained at a constant 78F (or whatever to suit the species) it becomes essential to have heaters in the tanks.
There are two significant reasons why more equipment will not resolve a problem in the biological balance of an aquarium. First, it is a fallacy that more filtration (in planted aquaria) is better. The less filtration the better for the plants. So having mega-filtration in a planted aquarium is actually making things more difficult for the plants and ultimately the fish. Plants have the ability to filter the water in a way that no mechanical filter can equal. And there is scientific evidence that increasing the water flow (with more filters, powerheads, etc) actually inhibits the plants ability to take up the essential nutrients. The result is less than optimum (and perhaps failing) plant growth, so the plants are not doing their best filtration, or they are themselves adversely affecting the biological system, and the filtration they should be doing is not being done by the mechanical filters, so the fish are negatively affected. There is a highly-interconnected circle in all this, and disrupting any aspect of that circle is going to impact the entire biological equilibrium. Which leads me to the second reason: the setup of a low-tech, or relatively low-tech aquarium is considerably different from a high tech, and in my view it is not possible to simply change course in mid-stream. The substrate is a major consideration, and while it is possible to modify an established tank either way, it is preferable to initially set it up with the entire system in harmony.
My remarks have been in general terms; if you are interested in specific applications I'd be happy to offer some suggestions from my research and 15 years experience with what I view as fairly low-tech planted aquaria; the photos of my "Aquariums" shows what they look like today.