Question: Water temperature and heating questions

I have two questions about the temperature of water. I have read from various sites that the temperature for axolotls should ideally be between 16C and 20C, however there are also sites saying that it is ok for the water to cool down to 10C during the night. There was even a book in the library saying this (it only had one page dedicted to axolotls though so I doubt its accuracy). My question is if it is ok to have the water fluctuate by 5 degrees or more during the day? I'm sure that it is better to keep it stable but will it cause any harm to the axolotls if it doesn't?

My follow up question is about heating, I still live with my parents who like to turn the heating down during the night because they believe that beds are warm enough (and I agree with that). During the winter the house cools down to 5 degrees though (the heating is still set to that to prevent plumbing from freezing) and I wonder if it would be necessary to have additional heating installed for the nights or would the water retain its temperature enough for this not being a problem? Personally I would play it on the safe side but I'm not even sure if it is even a problem at all, no sense in spending money on something you don't need

I hope to buy my aquarium in a few weeks after I've done some more research. I've even been to the library today to get some books, a place I haven't been in many years and I doubted to ever see one from the inside again!

I don't think you need worry too much about a heater. If the tank has a large volume of water it probably will not drop or rise too much. You could always cover the tank with a blanket to protect it a little.

Helloo axies dont really have a minimum temperature they love the cold but you are right to worry about temperature fluctuations (they dont like it at all aparantly!) but with enough water volume (id go for at least 3ft tank anything smaller and you may struggle to get a stable temp) it should hold its temperature well and shouldnt be fluctuating more than a degree or two overnight. My 15gal doesnt hold its temp probably about 5-6hours before its down to room temp but my 30gal does very well always very stable takes a day or so for it to reach ambient room temp so temperature fluctuations are not an issue just stays at the average temp of the room. I wouldnt worry tho its keeping the tank cool that proves to be the problem! I just cant imagine a heater in an axie tank, a full grow axie would smash one to pieces!

I'm planning on getting a sufficiently large tank, something which is at least 1m long (sorry, I use the more sensible metric system, multiplying by 10 is so much easier ), so it turns out that it won't be much of a problem, I'm quite glad of that when I do get a tank I will monitor its temperature closely though so it doesn't fluctuate too much. Better be safe than sorry