That explains it Marc
Had your water been RO/DI or something like that, you wouldn't have had the problem. Rain water is full of all kinds of goodies, but that is a whole other discussion that I alluded to in another thread
Organic Fertilizers
And no Philsuma it's not sterile, it's been opened and exposed to the air, clearly it's not sterile, but that has nothing to do with things growing in it. If it was tap water or something along those lines, it would already be growing things in it. However because it has a quick lifespan it will be sterilized and refiled before anything is a problem. Algae is not going to grow in it without the nutrients it requires to live. Bacteria will grow and form a biofilm on the tubing and other surfaces along the inside of the pipe if the pipe is left full of water, but they will be growing all over the insdie of your viv as well.
I understand this is something you heard, but the comment you made doesn't really make sense to me. I guess that means I am not familiar with it as I am not even sure what it is. I don't really understand what your trying to get at. Are you saying clear bottles are not safe? Or do you mean light is not safe for water? I have no idea what you mean or what it has to do with aerobic life. Even if it was in the dark, air would still be getting in there so what is the difference with darkness and light when it refers to Oxygen?