Join Date: Apr 2018
Location: Springfield, Oregon
It sounds like you might have a 20 gallon tall tank? You could use the empty tank that you have as a hospital / quarantine tank, if you get new fish that you are wanting to put in your tank that is currently running, it is always a good idea to quarantine them before adding them to your main tank, if you get fish that are sick you can separate them from the healthy ones and treat them in your hospital tank. To start out doing weekly water changes can be an important thing to start with, and making sure that the fish are fed, but not overfed. I doubt that the guppy is hurting the Molly, Guppies and mollies are pretty good tankmates from my experience, though if you happen to have a male and female Molly, or male and female guppies together they will breed like rabbits. If you have mini mollies in the tank it is possible that one of your females was pregnant at one time and gave birth. When you do water changes just remember to treat the water to make it safe for the fish, usually anything that treats it for chlorine but make it fish safe and there are plenty of affordable options on the market. I think you have a decent amount of fish for that tank size, so I don't think you're particularly overcrowded, you could also set up the second tank if you felt like you wanted to part the tanks out. Or if you wanted to raise a different type of fish you could use the 2nd tank for that. Overall have fun with it, this Hobby can be very rewarding and enjoyable! Best of luck!
Life without an aquarium is just flat out boring, Unfortunately like most in the hobby I'm highly susceptible to Multiple-Tank-itis.