Stocking density and stocking strength of an aquarium: One of the most important questions in the setting up an aquarium, except the Technology and the aquarium itself, the question is how many and which fish I should put in. This guide is all about how much. You read again and again how many fish I can put in a 54 or 60 liter tank. But it doesn't matter whether it's 54 or 60 liters. 100 or 120 liters or even 200 or 240 liter tanks. Even large tanks such as 300, 400 or even more liters have to take a few things into account when it comes to the number of fish. Sentences like “how many cm fit in my aquarium” which brings us back to the edge length and not just to the pure number of liters. But now step by step.
Stocking strength: factors of socialization
Before we get into the limits and rules of how many fish to put in, let's get down to ours Advice on socialization point out. You can find it here. There we go into the other factors that should be considered regardless of the number of stockings (the stocking density). These included, for example:
- social behaviour
- Territory formation
- Water parameters requirements
- origin of the fish
Please take your time and read this article carefully. It forms the basis for the selection.
Basic considerations
There are basically two different approaches to calculating stocking levels in an aquarium. On the one hand you can calculate this via the water surface, on the other hand via the number of litres. Both variants have their advantages and disadvantages.
However, the following applies to both variants:
- When buying the ornamental fish, these are mostly young fish
- Ask the retailer for adult measurements
- Find out the size of the parent fish
- Calculate the exact water content. Attention: Here you have to remove the decorative objects and also the substrate. This space is not available to the fish as a swimming space and thus also reduces the capacity.
- Calculate the water surface: length x width
Stocking density: Calculation of the number of fish above the water surface
The main advantage of this type of calculation is that factors such as oxygen uptake and carbon dioxide emissions are taken into account. This exchange only takes place at the water surface and has nothing to do with the number of liters. Take, for example, a square aquarium with a height of 1 meter. Here you usually have large amounts of liters in the aquarium but only a correspondingly small surface. In an aquarium with a height of only 40 cm, you get relatively little water in for a large surface. Therefore, this calculation can also make sense.
So they calculated the surface area, then it's time to determine how much surface area a fish needs. For this purpose, the length of the fish (when fully grown !!) is always taken. The caudal fin is usually not taken into account.
The following guide values can be taken as a basis in a freshwater aquarium. Attention with cold water pools or sea water pools, these can be completely different again.
Of course, there are controversial discussions about this and values are well above 30 cm2 or well below 30 cm squared.
For example:
You have an aquarium with dimensions of 60 x 30 x 35 cm, where 35 is the height. The water surface would then be 60 x 30 cm = 1800 cm2 surface. You could then divide this by the 30 cm2, which in turn will result in 60 cm. That's how many fish they could put in.
With an edge length of 2 cm per fish, this would then be a group or a school of 30 fish.
Stocking density: Calculation of the number of fish via the capacity
In addition to the calculation based on the surface, i.e. the water surface of the aquarium, you can also use a second calculation based on the capacity.
There used to be statements like 1cm of fish per liter of water. But you should say goodbye to this very quickly. No aquarium can be stocked appropriately with this.
Today, other values have prevailed, which are staggered according to the size of the fish. However, you will soon find out from our examples that these are not universally valid either.
Guide values
- less than 2 cm fish length 1 liter per cm fish length
- from 2 cm to 5 cm fish length 1,5 liters per cm fish length
- from 5 cm to 10 cm fish length 2 liters per cm fish length
- from 10 cm to 15 cm fish length 3 liters per cm fish length
- of 15 cm and more fish length 4 liters per cm fish length
Example
But let's look at some examples. Let's start again from our pool above with the dimensions of 60 x 30 x 35cm. The water content would be around 60 liters here, and this is where the first mistakes are usually made. Here you can not calculate the complete 60 liters, but still have to Furnishings, gravel, aquarium soil and a possibly lower water level. Values of around 45 liters are quickly reached.
If we now assume our 2 cm long fish again, then we could place around 45 fish of 22 cm each in 2 liters of water. In the above example there were around 30 fish.
You can already see that there are big differences.
But now an example that would never fit. Let's calculate with a 60 cm long fish. According to this formula, we would have to charge this with 4 liters per cm. So this fish would have to get by with an aquarium of around 240 liters. That would be pure animal cruelty and he would certainly not survive this for long.
Even if we assume a fish of 15 cm, which would mean that it can get by with around 60 liters. This would mean that only 240 fish of this species could be kept in a 4 liter tank.
Also note the height of the fish
So far we have not even considered the shapes of the fish. It makes a big difference if the fish also have a shape that is not only longer but also taller. From a height of approx. 2 cm, this factor should also be included in the considerations. The shape of the aquarium should also change or adapt here. High aquariums then have priority.
Calculation of the number of fish over the edge length of the aquarium
One reads again and again, especially in the wanted posters a minimum of edge length of the aquarium. But this has primarily something to do with the swimming behavior. A direct conclusion to the stocking density does not give this value. Nevertheless, it is important to note this.
As you can see quite nicely here, there is not one correct value and one correct calculation. There are much more different factors which influence the stocking. In addition, you should only use the above calculations as a rough guide. Because what's the point of not having made any mistakes when it comes to stocking density, but simply socializing the wrong fish that don't fit together.
The connection with algae, snails and other problems - overstocking
Beginners in particular usually see no connection between the stocking or the stocking density and, for example, an emerging one algae problem. However, this connection may very well exist. This usually happens when the aquarium is overstocked and the nutrients, perhaps due to overfeeding, take the upper hand. The different types of algae in an aquarium are happy about this extra nutrient and begin to thrive. Much to the chagrin of the aquarist.
Of course, there are other consequences of overstocking. Be it territorial behaviour, bad water parameters or fish kills. You should absolutely avoid this. Pay attention to the stocking density!
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