Theres been a lot of overcrowding issues and discussions around the board lately so I thought I would post this article. It will answer a lot of questions I think
Yes, it sounds like you are overstocked...by quite a bit. You go by the adult size of your fish, even though they may not yet be adults, aiming for a maximum of 1" of adult fish per gallon of water. 2 goldfish could work in a 10 gallon tank. However, Chinese algae eaters get up to 10-11", Mollies 3-4", and the cory around 3". That means you now have a total of approximately 27 inches of fish in a 10 gallon tank, which is way too much. In addition, goldfish are coldwater fish and should not be kept with tropical fish...there temperature and other care needs are just too different. I would suggest getting a new tank as soon as possible. Leave the goldfish in the 10 gallon, and move the tropicals into the new tank, which should be a minimum of 20 gallons. Also, just a heads up...chinese algae eaters, when they grow up, are very hard on other fish...they will literally chew holes in them. For the most part, just adding the 2nd tank you are already thinking about will help you a lot, but you may want to give serious thought to taking the algae eater back to the store.I recently bought a 10 gallon tank after winning a few goldish at a fair. It has already cycled and I decided to add a few more since the tank looked a bit empty. At the moment, I have two fantail goldfish (one 2" and one 1"), one 2" chinese algae eater, one 2" mollie, and a little 1" albino cory cat. I do plan on getting a 20 or 30 gallon tank in a few months since I figure my goldfish will be growing quite a bit. But is my tank considered overstocked since goldfish are so dirty?