I had two baby goldfish in a good 10 Gallon tank as their tempory home while I saved up to make a pond. One of the baby goldfish died after a water change and it was because of the drastic change from water temp. he's all alone in the tank and swims slowly and isn't his usual fast curious self. after the death I did regulate the water temp and tested the water and everything seems to be fine. should I get him another friend or just let the time pass?