Hi and welcome!
You can test evaporation with the simple bucket test. Fill a 5 gallon bucket with water and see if it loses as much water as the pool. If it does, it's evaporation and you should cover the pool when you are not using it.
Otherwise, you have a leak and need to be a bit of a detective about finding it. First: Do you notice it loses the same amount of water when the pump is running as when not? If it loses more when the pump is running, examine every fitting and hose, pump and filter for wetness--a sign it's leaking. If it's not there, then search the area around the pool for dampness, both the ground and the pool walls. If you find it, that's the area to localize your search.
To use the find-a-leak dye, you need to turn off the pump and let the water get very still. Add dye in the area you suspect it's leaking and add enough. Wait. If there's a leak, the dye, after 10 min to an hour, should collect there showing you the hole. Then you can patch it, using patches and Boxer 100 glue, which works underwater. If you have extra liner left over from your install (if you did an overlap liner) or kept some of the old liner, that makes excellent patches. I always double-patch. First has an inch of material on all sides of the hole. Second has at least an inch of material all around the first patch.
Underwater patching is a pain in the neck, all way down, but it's do-able and the patch is permanent.
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