If one is new to fishkeeping, stocking is best looked at not by numbers but rather by water clarity. Slowly add some fish. Then see how it goes. Keep looking down the length of the tank and judging how clear the water is. If the water looks even a little bit cloudy do not add any more fish till the cloudiness clears up. Don’t worry about numbers. Gage the stocking by the health of the tank. How clear is the water? When the water is clear, add more fish. Cloudy water? Wait a while, till the cloudiness or “dullness” clears. Then you can add more fish. Simple!
Stocking and Opinions
The topic of stocking is largely OPINIONS, not experimentally derived scientific facts. Let me repeat that:
The Topic of Stocking is Largely OPINIONS
So do what YOU want to do with YOUR aquarium. If you want some guidelines which are largely just my opinions, read on.
The Science
Note that there is some science here. And the science says that VERY VERY HEAVY stocking of aquarium tropical fish is quite healthy and does little harm to tropical aquarium fish. The science is based on university research on the zebrafish and can be found in the following article:
13.2. Calculating Stocking Ratio
My Opinions and Recommendations
IN MY OPINION, the following stocking ratios, based on the volume of fish, are perfectly acceptable for a 100 gallon tank:
Number of fish for stocking in a 100 gallon or 378,54 liters aquarium
| Total length of fish | Light stocking | Recommended 100% level stocking | Heavy stocking * |
|---|---|---|---|
| 1in 2,5cm | 181 | 630 | 1890 |
| 2in 5cm | 28 | 93 | 280 |
| 3in 7,6cm | 10 | 32 | 97 |
| 4in 10cm | 5 | 17 | 50 |
| 5in 12,7cm | 3 | 11 | 33 |
| 6in 15,3cm | 3 | 9 | 27 |
| 8in 20,3cm | 1 | 4 | 11 |
| 10in 25,4cm | 1 | 2 | 9 |
| 12in 30cm | 0 | 1 | 3 |
| * ONLY with very heavy filtration | |||
For a 50 gallon tank the stocking numbers are:
Number of fish for stocking in a 50 gallon or 189,27 liters aquarium
| Total length of fish in centimeters | Light stocking | Recommended 100% level stocking | Heavy stocking * |
|---|---|---|---|
| 1in 2,5cm | 90 | 315 | 945 |
| 2in 5cm | 14 | 47 | 140 |
| 3in 7,6cm | 5 | 16 | 48 |
| 4in 10cm | 2 | 8 | 25 |
| 5in 12,7cm | 1 | 5 | 16 |
| 6in 15,3cm | 1 | 4 | 13 |
| 8in 20,3cm | 0 | 2 | 5 |
| 10in 25,4cm | 0 | 1 | 3 |
| 12in 30cm | 0 | 0 | 1 |
| * ONLY with very heavy filtration | |||
For a 25 gallon the stocking numbers are:
Number of fish for stocking in a 25-gallon or 94,64 liters aquarium
| Total length of fish in centimeters | Light stocking | Recommended 100% level stocking | Heavy stocking * |
|---|---|---|---|
| 1in 2,5cm | 45 | 159 | 492 |
| 2in 5cm | 6 | 23 | 90 |
| 3in 7,6cm | 2 | 8 | 24 |
| 4in 10cm | 1 | 4 | 12 |
| 5in 12,7cm | 0 | 3 | 8 |
| 6in 15,3cm | 0 | 2 | 7 |
| 8in 20,3cm | 0 | 1 | 3 |
| 10in 25,4cm | 0 | 0 | 1 |
| * ONLY with very heavy filtration | |||
For a ten gallon the numbers are:
Number of fish for stocking in a 10 gallon or 37,85 liters aquarium
| Total length of fish in centimeters | Light stocking | Recommended 100% level stocking | Heavy stocking * |
|---|---|---|---|
| 1in 2,5cm | 18 | 63 | 189 |
| 2in 5cm | 3 | 9 | 28 |
| 3in 7,6cm | 1 | 3 | 9 |
| 4in 10c | 0 | 1 | 5 |
| 5in 12,7cm | 0 | 1 | 3 |
| 6in 15,3cm | 0 | 1 | 2 |
| 8in 20,3cm | 0 | 0 | 1 |
| * ONLY with very heavy filtration | |||
For a five gallon the numbers are:
Number of fish for stocking in a 5 gallon or 18,93 liters liters aquarium
| Total length of fish | Light stocking | Recommended 100% level stocking | Heavy stocking * |
|---|---|---|---|
| 1in 2,5cm | 9 | 31 | 90 |
| 2in 5cm | 1 | 4 | 14 |
| 3in 7,6cm | 0 | 1 | 4 |
| 4in 10cm | 0 | 0 | 2 |
| * ONLY with very heavy filtration | |||
The heavy stocking columns for the ten and five gallon aquariums have been crossed out for a reason. The filters for small tanks are always very small cartridge or air operated sponge filters. These filters are just totally inadequate to support heavy stocking. So small aquariums should not be heavily stocked. If one puts something like a very small canister filter on a ten gallon, one can think about heavy stocking. But I’ve never seen that done.
Now these numbers, especially the “heavy stocking” numbers, will absolutely send some “fish police” into absolute hysteria and get this site kicked off many Facebook forums. Remember, the heavy stocking levels are only “ MY OPINIONS” (not “rules”) based on WELL FILTERED AQUARIUMS WHICH HAVE LARGE FILTERS WITH GOOD MEDIA THAT HASN’T BEEN FREQUENTLY CLEANED!!!!!
In the in depth articles below I give my OPINIONS on the topic and the OPINIONS of others. It is all a rambling set of OPINIONS so unless you want to get really bored, stop right here.
Stocking in Greater Depth
Hopefully the following links can put some common sense into this subject:
13.2. Calculating Stocking Ratio
And the common or narrow bodied goldfish should be stocked as a five inch fish.
This is delved into in this link:
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