Yeah chances are good that would push you dangerously past the 10G tank limit. Any of your fish died? Even the rainbow's would come out to total about 10.5 inches right? I try to go with at least a gallon of water per inch of fish. What does the water quality look like? I know some pet shops do free water tests if you bring in a sample. You want to look for nitrates and ammonia as these will kill your fish.