When our children were small, the issue of a killifish or livebearer dying came up. I admitted to them that some fish die early because we didn't take care of them as well as we should have. However I also tried to make it very clear that if a fish just kind of stopped acting vigorous, showed obvious signs of aging and died between one and two years of age, for many of those fishes, that was the time "God gave them." And it was a lot better than the three or four months they might have in nature before something ate them.

They were cool with that and handled a certain number of fish casualties with aplomb. She had her golden bodies, red delta guppies and he had his Fundulopanchax gardneri Misaje.

Her's were something like the following, though certainly not as big:
http://www.chesapeakeguppyclub.org/Gold%20Red%20male.jpg

His were close to this:
http://www.chesapeakeguppyclub.org/Gold%20Red%20male.jpg
And his gardneri finished higher than any of my killies in one show.

In some cases when a certain fish died, I was the one who got upset.  "AArgh! I never got around to saving fry!" (Or eggs, species depending.) ;)

Cloudy water and sometimes greenwater are blooms of bacteria in the first case or protists in the second. They are living upon excess organic "stuff" in the aquarium. Usually there is some uneaten food, some dirt that got buried in the gravel, dead plant material or some detritus, which lodged behind the box filter or a rock.

Do an extra partial water change. Use that gravel vacuum and try to poke around in a number of likely spots. Most aquarists run into something like that from time to time. Sometimes we find the  cause, sometimes just general house keeping helps the problem fade away.

Greenwater is a little more tricky. In Immediate Help, under "Water (cloudy/green etc.)" you will find more info.

Rare is the aquarist who can't do a little more help their water quality along. You have brought some troubled guppies back when they were hurting. Don't be too hard upon yourself if an elderly guppy dies of old age. :)