I have a 10gal freshwater tank with a filter for a 20gal tank, 3 guppies, 1 female betta, and 1 emerald cory. My water temp is is at 75 and I keep my PH at 7. Everyone is happy and healthy. I am thinking about either adding another fish or setting up a new tank. Any suggestions? I have had a freshwater tank for 20 years and have never had a saltwater tank.