Suggested definition for fish load levels.

[vidiots]

Hi Tom,
I have noticed that a number of aquarium articles refer to fish loads as light or heavy, but most do not define what light or heavy is leaving that to the reader to determine for themselves. I wanted to propose possible definitions for these and see what you thought of them.
I was thinking that NO3 produced by the fish and other critters per week would be a good way of defining this. The number of weeks between 50% water changes required to maintain nitrate levels below 40ppm as the cut off for each category. Example:

Very Low or Light fish load = 40ppm NO3 per week = simply ridiculously over stocked.

 

[VaughnH]

How do you calculate the amount of NO3 produced by a fish? And, if a tank is heavily planted with healthy growing plants, the plants will use up the nitrates without a water change being needed. (Up to some limit, of course.)

 

[vidiots]

How do you calculate the amount of NO3 produced by a fish? And, if a tank is heavily planted with healthy growing plants, the plants will use up the nitrates without a water change being needed. (Up to some limit, of course.)

First I wasn't suggesting this be used as a rule for stocking the tank, as there are too many other variables to consider to use this in that way. But more as a standardized method for describing what we mean when we say a tank with a light or heavy fish load.

For someone to determine this for themselves they would have to measure the amount of increase in nitrates over a week period, and eliminate the other factors that would offset their measurements. It asumes a fish only tank with no plants or algae and accurate measurement of the nitrate level.

The fish load will be the same reguardless if we put plants in the tank, although it becomes too tough to measure with the plants. Even if the conditions are better if you have plants consuming the nitrate.

I think that the majority of hobbyists start out with fish only tanks and later add plants. Many of us also have planted and non-planted tanks so we can still get a good idea of the fish load.

 

[vidiots]

I just had another thought that the opposite could be used to quantify what we mean by a heavily planted tank, lightly planted tank, balanced tank. By using the amount of nitrate consumed. Although that one will require some more thinking about how that would be classified and if it would even work...

 

[morphriz]

Things things dont lean well towards consice definitions. I suppose since there is no use for a "real" definition. The "lenght of fish per volume unit of water" have served the aquarium community for along time as the closes we get to actually determining fish load. A more scientific way would be to weigh you fish and that only works for small fish.

The NO3 measurment is actually real bad one, good idea though. It's bad since it's a measurement of biological activity both in the fish case and in the plant cast. Fish depend on amount of food, water temperature and seasonal activity level to determine their metabolic rate(which in the long run becomes the amount of NO3 produced). Plants depend on light and availability of other nutrients to determine how much NO3 they consume.

So if we kill the fish and dry the plants we could make an educated estimate, but what would we need it for by then?
cheers
//Mattias

 

[Tom Barr]

I have a very tough time suggestion any standard here.

I've used the 1" per gallon rule as standard loading.
But........that suggest that you feed the same as everyone, that you have the same type of fish, say a 14" Oscar vs 14 1" cardinals are not the same.

I think that the fish loading might be better described via the amount of food one adds in terms of a dry weight. But here again, mots/many feed wet frozen or live foods etc. There is just too much variability to standardize all this.

For sake of discussion, I use such general terms. I have to, to talk about it.
Having said that, I Use a 1" of small fish load as my standard. Few keep really large fish in planted tanks. I use typically feeding: some Frozen brine(1-2x a day, what they can eat in 5min) and 1-2x a day flake.

Discus are about the only larger commonly kept fish.
They are my large fish standard and I have a lot of experience with them.
Big overfed cichlids after all...........

I go about one per 15 gal, some have gone to 1 adult per 10 gal in well run moderately lit tanks with 2x a week water changes.
I required about 1/2 the KNO3 as normal in such tanks(2.2 w/gal PC lighting).

So 50% of the N came from food.
Still, you have 2x the required K+ before it becomes limiting with KNO3 dosing.

If you exceed this bioloading, then algae and GW plagues become issues, it's also just not right ethetically to cram so many fish in the tank and demand stable plant growth and O2 production, night drops in O2 levels etc.

As you add more and more light and more and more fish, things become much harder to balance.

Folks need to back off those and balance things better in those respects and not worry so much about NO3/PO4.

Then NO3/PO4 are not issues and you have to add them vs doing lots of water changes etc. But folks like the CO2 gas, higher fish loads and higher light............so we do water changes.

Amano does large water changes every 2-3 days for the first month or two of a new tank set up. I do them about 2x a week, Jeff Senske about every 4-5 days.
We all came to that independently also.
I tend to have the highest bioloads.

Regards,
Tom Barr

 

[fauxjargon]

I think a valid formula is ((Fish length + 3)/4)^3 = gallons per fish. I don't worry too much about high bodied fish as they tend to be laterally compressed compared to an equivalent length torpedo-shaped fish.

For example, using this formula:
1" fish = 1 gallon
2" fish = 1.95 gallons
3" fish = 3.5 gallons
4" fish = 5.35 gallons
5" fish = 8 gallons
6" fish = 11.4 gallons
7" fish = 15 gallons
8" fish = 20 gallons

Based on the idea that the body mass of a fish increases according to the cube of its length.