First off your tank isnt too small. Rule of thumb is what ever gallon the tank is the amount of inches of fish can be house in it. For example 10 gallons 10 inches of fish. Your tank is prefectly fine for what you have but i would not add anymore to it. The fish that gave birth are most likely guppies because they can produce young very often and very frequently. Because you have more fish there is more waste which means your nitrates could be high, i would suggest maybe buying a more powerful filter. And the plasic container the above person is talking about is actually a container for livebearers or other fish that dont care for their eggs/fry. Change your filter and make water changes once a week at about 20% and i can guarantee your fish will live. But if you plan on keeping your guppies i suggest you buy one of those breeding containers because you will keep 100% of your young and you will be able to keep them and you may even be able to sell or trade in for things at your local pet store. ... View related article.
First of all to take a closer look maybe get a see through container and fill it up with the tank water and net the fish and look at it closely. What gallon tank and what type? It may be a female and may be pregnant. Also it may have ich (looks like dandriff on the side of the fish). If that is the case remove the fish into what we call a hospital tank or something that can hold it til it is cured. At the local pet stores the have a ich remover solution. ... View related article.
