 Re: Bioload
Not only how many things that are living in the tank, but accumulation of the waste they produce. Some fish produce more waste than others.
Basically, the more fish you have in a tank and the more you feed them, the high your bioload...the biological strain on the filtration system of your tank.
A higher bioload means you need to change the water more frequently, have better filtration and keep a closer eye on your tank. There is not real "limit" to a tank, but there are reasonable guidelines for how much bioload a tank can handle based on: tank size (water volume), filtration (skimmer, filter) and biological filtration (live rock and live sand).
Smaller tanks obviously have less water volume and therefore are more sensitive to an increased bioload.
The amount of fish that a 55 gallon tank would be able to handle (like is in your tank) will easily and quickly overcome the filtration ability of a 10 gallon tank.
Adding better filtration, more live rock and more frequent water changes are only a few ways you can help the situation.
The most important thing is to be responsible with what fish you keep in your tank...making sure they are appropriate for the size tank and making sure you have enough filtration ability in the tank. | 
Bioload 
