O.K., please nobody yell at me!! I have coldwater and tropicals in my 30 g., see below. Now, I realize that they have different needs, etc., and I will eventually have another tank to divide the two types. I (unfortunately) got my goldies under recommendation from someone who didn't know what they were talking about and before I knew better. Now they're wonderful pets and I could never part with them, yet I currently lack the space and cash for another tank. So, I am very VERY careful about monitoring my tank until I can do something about my predicament. My goldfish are living in the warmer end of their acceptable spectrum, and my tropicals are at the cooler end of theirs. As for food needs, there are several things that everyone loves,
brine shrimp, bloodworms, and veggies. Then, I feed their flakes, etc. different times, tropical after goldies because the goldies are pigs.

Thus far, my situation is working out quite well. It's not ideal, but it's working temporarily. Guppies wouldn't live 15 minutes in my tank. My goldies have eaten two smaller fish in the past and I think they would do it again. The moral of my story is: GO TO FISHLORE.COM AND GET EDUCATED BEFORE BUYING FISH!! It's a wealth of knowledge on here!