Sorry, this is a bit long. I'm finding myself confused on how much of a problem temperature fluctuation actually is. There are obviously a lot of threads about it here, and a recent trip to the LFS also made me concerned about it. Most of what I read here says it's not a big deal. In short, the temperature in my tank has been ranging from about 78 to a little over 80F when it's hot outside (it had been closer to 82 at times, but I bought a small fan that I turn on if I see it up around 80 now). It is a small (6g) tank, so it doesn't take much to change the water temp I guess. I live in an old house and the tank is on the second floor; even with the AC on, the second floor gets pretty warm. The tank doesn't get direct sunlight. [The longer story: I had a couple of newly acquired pygmy cories that were flashing and acting strange. I went to the LFS to ask about it, and they asked about the tank temp. They said the temp fluctuation could lead to issues such as ick. I think they may have misunderstood when I told them the temp range was 78-80, because they suggested I get a heater to keep it at 78 for 2 days and see if the fish seemed better, and the heater they sold me was a preset for the 76-80 range. (And how is this range not problematic if a 2-degree fluctuation is an issue?) Obviously, water that is too cold is not my problem right now. And, FWIW, the person I worked with at the LFS is very knowledgeable and has been in the biz for decades. Ultimately I never used the heater; over those 2 days the tank temp was consistently at 78 anyway. (Ultimately, one of the fish died and the other ones now seem fine. The one that died was very small and didn't seem that great from the beginning.) I returned the heater and will get another (better) one if needed when the weather cools.] Here's the thing: I just can't be obsessing over temperature change all day long. I can't monitor it all day and all night. The temp in that room is going to change throughout the day. When should I be concerned? When is the normal fluctuation of the temp throughout the day a problem? I want to do right by my fish, but I just can't handle obsessing over so many details. If this isn't the hobby for me, then I would rather know that now. We would like to get a bigger tank (~30 gal) soon, and if the temp in my house is going to be a big issue for a bigger tank as well, I would rather know that now so I can reconsider. Will the fish be okay as long as they are established in the tank? That is, am I better off just adding fish in seasons when the temp is steady and not in the hot summer months? Thanks in advance for any advice. I just don't know what's problematic or not at this point.