I bought a torch that has a 365nm UV light, which I believe is UV-A?

When doing a poke around my house to see what I could see with UV, I noticed that my freshwater fish tanks looked “cloudy” / “milky” under UV, yet they are crystal clear under normal light.

I checked tap water and bottled water with the same torch and they do not react and look perfectly clear under both UV and normal light

I also have an auto top off for one of the tanks which is full of ~50L of a mix of RO water and tap water treated with dechlorinator and this also does not react.

I have 3 tanks inside of various volumes (700L, 150L, 20L) and various stocking levels which all show the water as a pale flourescent green colour under UV. The colour is uniform and completely spread out through the water volume, not concentrated on any area or in layers or whatever.

The currently empty 20L tank reacted the least, leading me to believe that it may be some sort of organic material that is causing the UV light to react so much?