Ratio between fish size and gallons of water

jcb

jcb

Member
What is the appropriate amount of water that should be allotted for every inch-measurement of fish? I've been told anywhere from one gallon per inch, to 10 gallons per inch. Quite a discrepancy, don't you think. Could I get a few of you to give your expert opinions? Would really appreciate it....
 
W

wrassefan

Guest
It depends on the "potential" size of the fish. A juvenile emperor angel could be only 3" when you first buy it but will eventually grow to 8". So the answer is it depends on what your plan is. I sometimes buy a fish knowing I will have to trade it in to the LFS just because it is growing too big. I usually allocate 6 gallons per fish if I buy them when they are 2". That way I will have the fish a few years (hopefully) before I would have to trade it in.
 
ja

ja

Member
The general rule of thumb is 1" of fish for four gallons. So if you have a a 4 inch fish you will need 16 gallons for that fish. Also you need to measure the fish from before the tail fin to the tip of its nose. Not the end of the tail fin that will give you a little more leaway with the size of the fish. I have two four inch fish in a 30 gallon tank and I can not get any more if I dont want any problems. Although a few inverts could be added because their metabolism is very slow and they do not contribute to the breakdown of the tank that much. The reason why so may people have problems is that they add too many fish to their tanks. There can be only so much biological filteration depending on the size of the tank.
 
clownfish

clownfish

Member
It really depends on a lot more than surface area and waste products. These are the factors, IMO:
current size of fish
potential size
fish temper and territoral needs
digestion efficiency
O2 concentration in water
amount of live rock, caulerpa, etc to remove nitrogenous wastes and other wastes
volume of tank
vertical and especially horizontal room to swim
protein skimming
and so on
These factors determine the max number and size of the fish that can safely live in a tank. I will set up a 55 reef in September. These are the fish I plan to have in it:
tomato clown (awesome)
coral beauty (awesome)
a few small damsels
perhaps a yellow tang
 
jcb

jcb

Member
Hey, guys. Thank you very much for your detailed responses. One question with regards to surface area, though: Does the surface area of the wet/dry container count as well?
 
jcb

jcb

Member
O.K., I now understand that surface area is vital to the amount of residents that can be safely kept in a tank. What can over-population do to your fishes? What are the signs to look for. I must admit, if I go according to the "one-three-inch-fish to one-square-foot-surface-area" ratio, I have over-populated my tank by two 3-inch fishes. I feel like if I've comitted some-kind of an animal cruelty act. What should I do?
 
kris

kris

Member
O.K guys, enough with the tecnical junk, throw out the "inch per gallon rule" and don't bother getting out the calculator for determinig surface area, here's what I do--Add fish one at a time, after each addition wait a month--are they fighting over food or hiding spots?, are your normally quiet fish racing around? Has the water quality suffered at all? If all your answers are no, add another, continue till 1 or more of your answers are yes.
 
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