temp fluctuations

So I've been keeping fish for quite a few years now and this is an issue I've never seen. When I woke up this morning, My fish tank was around 78f and now, only about 4 hours later, it is cold enough the thermometer is not picking up a reading. The thermometer has very limited range, 50f-100f...

I heard that heaters could break easily, but mine has a 15-year guarantee so I'm not too worried about it. It has the temperature on it but that can be a little hard to read, so I have a stick-on external temperature marker. Idk what else I'd use. The heater lights up when warming up the water.

im planning to get a betta in a 2.5 planted tank but im keeping it in my room with AC, i turn my AC on sometime when its hot, im planning to get a heater but still... how the heck can i avoid temperature fluctuations in an AC room even with heater?

I’m fighting my own brain again , this time of year the only thing I really monitor on my tabk is temp, battling the elements to keep that green zone of 76-80f yet my logic is saying to me there is no possible way that the South American river system in winter months is at this temperature, I’m...

I’m having temperature related worries at the moment my tank has always been set at 26.5-27.5 I keep South American fish so maybe on the higher side but that’s what there used too n lately with the season changing I’m struggling to maintain it , iv woke up this morning to a temp of 25.1 both...

In the summer months the ambient temperature around my tank fluctuates a lot, the tank temperature goes from 75-77 degrees quite a bit. I’m wondering if this is okay for my fish? If not is there any way I can keep the temperature more steady?

So, a friend of mine and I are setting up a South American biotype tank at school, and we have narrowed our selections down to this: 20 or so bloodfin/rummynose tetras 20 or so cardinal/neon tetras 12-15 trilineatus corydoras 1-2 bristlenose pleco We have a 110 US Gallon tank, with plenty...