The tank where Amos lived was well planted - the plants being a significant part of the attraction of the tank. Getting plants to grow in a tank can be more difficult than keeping fish happy, so I've written a bit about how I do it (and why I think it works).
There are pictorial sequences of when I last moved house and setting up the five foot tank both of which include step-by-step photos of setting up a tank for plants.
Getting plants to grow in a tank is actually somewhat more difficult than satisfying fish. There appear to be two main limiting factors. Firstly, the amount of light in a tank, though it may be plenty to see the fish, is rarely enough to grow plants. Secondly, of all the possible nutrients that could limit plant growth, it seems that carbon dioxide (CO2) is the most critical.
Getting more light into the tank is relatively easy. Most fishtanks are lit with fluorescent tubes, and in theory it's simply a matter of packing more in. The only real problem is that most tank hoods are not intended to accommodate more than one or two tubes, so some surgery may be required to fit in a few more. The subsequent problem is accommodating the light controller, which is typically a bulky, heavy box belting out a fair amount of heat. Basically, just hide them where you can.
With big (especially deep) tanks, it may not be possible to get enough flourescent tubes in. In this case, there are various other types of lights which provide more intense lighting than fluorescent tubes. Although these are commonly used in marine, coral reef tanks, they are relatively rare in freshwater tanks. The five foot tank I have, which is more than 2 feet deep, uses just such a light - it's a 'metal halide', which is a variety of gas discharge lamp. These come in various colour temperatures - for freshwater plants (as in this tank) I use one of around 5000 K.
Respiration is the process of liberating energy in the cells of a living organism by breaking down a food molecule. The simplest of the possible reactions features one molecule of glucose plus six molecules of oxygen being converted to six molecules each of carbon dioxide and water:
C6H12O6 + 6O2 => 6CO2 + 6H2O + energy
Photosynthesis is the process of using energy from sunlight to convert simple molecules to more complex carbohydrates. The simplest reaction here bears a striking resemblance to the respiration equation above:
energy + 6CO2 + 6H2O => C6H12O6 + 6O2
All animals and plants respire. In every cell of their bodies, all the time, they are consuming oxygen and liberating CO2. However, during daylight plants are also photosynthesising. If they are healthy, the plants will photosynthesise faster than they respire, and overall a plant in the light will take in CO2 and give out oxygen, but they _are_ consuming oxygen at a cellular level. In the dark, the plant continues to respire, consuming oxygen, but the photosynthesis stops, so overall a plant in the dark takes in oxygen and gives out CO2.
If a plant can't get enough CO2, it won't photosynthesise as much as it could, it won't build up a healthy food store to see it through the night, and it will gradually die.
It is worth noting that although carbon dioxide and oxygen are on opposite sides of the equations above, there is nothing that forces a particular balance in the water of fish tank. That is, high CO2 levels do not automatically mean low oxygen, and vice versa.
Fish in the tank obviously require a certain level of oxygen. However, as noted above, that does not preclude a particular level of CO2. At any reasonable level of CO2 the fish are not upset. Indeed, testing my tanks reveals a higher oxygen level (close to saturation) in densely planted tanks than in less planted tanks.
In order to elevate the level of CO2 in the tank, I use a carbon dioxide injection system. This takes CO2 from a pressurised cylinder, feeds it through a pressure regulator and a needle valve and 'drips' it into the tank.
The system I originally set up was sold specifically for fish tank use. However, I have since substituted a much larger CO2 cylinder (bought from a welding supplies shop), and I think that if it were done with ordinary industrial supplies (cylinder and regulator from welding supply shop, a needle valve and various fittings maybe not so easy to source, but not impossible) it'd be a lot cheaper.
My setup was made by Dennerle, and used a cylinder containing 350g of CO2. The going rate to refill this in an aquatic shop (around here anyway) is about 8gbp. A welding supply shop confirmed the connection was a standard size and sold me a tank holding 6350g for 88gbp, and will refill that for about 25gbp. So that's more than 18 times as much CO2 for 3 times the price, and needing less frequent refills. The only disadvantage is that the cylinder is too big to fit inside the tank stand (it stands about 820mm high). It's a bit industrial looking, so I have it in next room with a small hole through teh wall behind the tank through which the supply pipe passes.
From the markings on the cylinder, this is principally intended for food use (in a pub cellar). Any of food, industrial or medical grade CO2 is pure enough for fish tank use. Fire extinguisher grade need only be 99.5% pure (according to some BS code of practice I found once). This might be pure enough, but I don't know for sure.
The process of getting the CO2 from a gas into solution in the water is relatively straightforward. CO2 dissolves in water fairly easily (at the levels being dealt with here), so the gas is held in a diffuser where it forms bubbles past which water is circulated (from the return from the filter). It dissolves in the water and is therefore dissipated throughout the tank.
This photo shows my home-made diffuser. A pump in teh sump sends water through the larger green hoses, entering the diffuser by the hose at the top. This feeds into a venturi aerator, which directs a jet verticaly down an inner tube. Six rods cross teh tube at various angles to cause some turbulence. The water leaves teh diffuser from teh bottom, and heads off into teh tank.
The CO2 is introduced by injecting it into teh water flow before the diffuser - you can see the green air-line size pipe directed into a T-piece to the left of teh picture. This pipe has come from teh CO2 cylinder in teh adjacent room, via a hole in the wall.
The inner tube is contained within a larger diameter enclosure. Any bubbles jetted down far enough to escape teh inner tube find slower moving water and start drifting up again. If they miss the inner tube, they drift up past it to teh top of the diffuser. Here, the venturi aerator has an inlet which sucks them back into circulation.
To be honset, this is overkill. I pump enough water through that I
could just have the outer enclosure to catch the injected bubbles in
one place. I think the CO2 would swirl
around and diffuse itself. However, when I built the unit I didn't
know it would be that easy!
Of course, there are other factors that promote plant growth. The tank filtration, the substrate and various other nutrients and trace elements can help healthy plant growth.
The filtration in a plant tank needs to be chosen so that it does not counteract the other effort invested in plant promotion. In particular, CO2 will come out of solution in the water as easily (or more so) as it went in. Filters that feature lots of turbulence, or promote excessive gas exchange will therefore let the carefully injected CO2 escape to the atmosphere. For this reason 'trickle' or 'wet and dry' filters are not normally a good idea. Large, slow-running fully flooded filters are better. Violent filters are also prone to oxidising the nutrients from fertilisers added to the water, making it more difficult for the plants to get what they need out of solution.
The second problematic filter is the 'undergravel'. This is constantly drawing water through the gravel at the bottom of the tank. Plants just don't like it. They will grow, but much more slowly and less vigorously than they would without the flow. I think the roots have evolved to like stationary water around them, possibly with a very low level of dissolved oxygen, and the undergravel filter just doesn't let this happen. Note that there are plants, notably Java Fern, which don't mind flowing water on their roots. Indeed, Java Fern grows best with its roots exposed, clinging to the surface of a bit of wood or rock, much like ivy growing up a wall.
The smaller the grain size, the better. This makes sense, since in the wild aquatic plants are mostly growing in layers of silt. The barren layer of large-grained gravel in most fish-tanks is not at all what the plants evolved to expect. A good compromise is silver sand, which is not messy as silt would be, and doesn't seem to upset plant roots too badly. However, even sand can be difficult to maintain, so a very common solution is to have a layer of fine (1 to 2 mm grain size) gravel on top of the sand.
The second aspect of substrate has been alluded to already. Clean sand or gravel is not particularly nutritious. No-one would dream of trying to grow roses in a bed of gravel - they get fertilizer and manure and who knows what. Similarly, it helps the plants tremendously to include some sort of food in the substrate. Normally mixed into the sand, or placed in a layer beneath it, this can be a number of things. Personally, I only have experience of a proprietary additive - 'Aquaponics Substore', so that's the only one I'm going to mention. It looks like potting compost (it probably is mainly potting compost) and is mixed in with the sand in the bottom layer.
If the substrate is enriched, it is important to ensure that the layer does not start to rot. This is most commonly achieved by putting the substrate on top of a low power heater cable. This sets up very slow convection currents within the substrate layer, causing just enough water movement to prevent anything going anaerobic and poisonous.
Iron is an essential trace element. Lack of iron results in leaves losing their green colour and disintegrating. It makes for a very untidy looking tank. A well planted tank needs fertilising (it's not a perfectly balanced closed system) and I always use a fertiliser that's got a good level of iron in it.
To comment on anything (please do) email ian.web@astounding.org.uk