Question: New tank fan for cooling causing water level to drop "quickly"

Hello all! I'm a new Axolotl owner (soon-to-be at least, I bought his tank on Monday and will pick him up tomorrow). I've set up my 10g tank with large substrate, filter and hood. I noticed earlier in the week that my tank was at a constant 76F. I know the optimal temperature for an Axolotl is below 74F, so I did some research into how to cool the tank.

I ended up ordering this fan from ZooMed and it arrived last night. I set it up last night and let it run through the night. When I woke up in the morning, the tank temperature was down to a nice 73F and I was happy about that. However, throughout the day I've noticed that the water level has dropped relatively quickly. I don't mean it's dropped tremendously, just noticeably.

My question then is two parts. First, is this normal for this method of cooling, and is this just a necessary inconvenience for cooling his tank? And secondly if it is necessary, how would I go about restoring the water level. I know just adding more water might be bad because it might contain chlorine or not be cycled properly, but is there a way to quickly cycle water before adding it in? Can I condition it beforehand? Or is just adding a little bit to keep the water level up okay? Any and all help is greatly appreciated, thanks!

The temps for axolotls shouldn't get above 72F for any significant length of time; "optimal" is really more like 68F or less.

Another option, although more expensive, is to use a chiller to control water temps.

Water doesn't become cycled, your aquarium filter does. And it usually takes weeks to do so. See this:

The (almost) Complete Guide and FAQ to Fishless Cycling - Aquarium Advice - Aquarium Forum Community

If you don't fishless cycle the tank filter before getting an axie, you're going to be doing massive water changes each day for quite some time until your filter becomes cycled.

You do want to condition your water before adding more to the tank, by treating it to remove chlorine or chloramines, depending on what's in your water supply (they are different). This usually also removes heavy metals.

Another good source for info is axolotl.org

Thanks, I will give both of those websites a look. I did see the aquarium chiller option and it out of my price range for right now. I have used axolotls.org before, that is where I found the idea for a fan.

The fact the water level drops does indicate you are getting significant evaporative cooling. The disappearing water is taking with it into the air approximately 620 calories per gram of water that goes. It is probably best to dechlorinate a jug or tub of water and use this for topping up. You need to do partial water changes as well as continually adding tap water without changes will result in concentration of salts in your water within the tank.

Partial changes are also needed while cycling becomes established.

The whole point of a fan is it cools by evaporation, so a drop in water level is normal.

Your cycle lives in the filter (and some in the substrate and on ornaments etc) not the water, and any water added must always be dechlorinated (conditioned) before you add it to your tank.

Best practice would be to do a water change and remove some of the tank water before topping up. e.g. 50 L tank - 3L lost due to evaporation, remove 15L for a water change, add in 18L to top up.

I'm pretty concerned about your use of the words "large substrate" what do you mean by that?