Unfortunately there wasn't much you could do about those things and the damage was probably permanent. You did most of what your could.

I don't think that anything in Immediate Help would refer to this. If you Mom' guppy was over a year old (figure 3-5 months before you purchased her) this could also be a part of aging or at least aggravated by aging.

Ah... this is a recent purchase. Remote as it is, was the fish just put into very different water? Was the water treated and allowed to site a while before adding it to the tank. Really cold tap water can release a lot of carbon dioxide and nitrogen. As this gets into the fish's bloodstream, it can mess them up much as the bends can effect and even kill them as it can kill skin divers that ascend too quickly in the ocean.

That all of your fish didn't go into convulsions makes one wonder if it was the water. Even water departments have been known to dump something new into the water without informing people. If no other explanation presented itself and all of the fish were shocked, I would call them and ask what changes were made in preparing the water. (It is very rare and sometimes maybe a part of hobby folklore, but aquarists have left their hobby after all of their tanks were wiped out by something in the water.

So that we don't see things like that, we need to   feed a variety of "fresh" foods. Flake foods should be used up within a couple of months because some vitamins (especially C) will be progressively lost after the package is opened. I would suggest that the diet include some vegetable items. If a guppy flake combo is used, veggie flakes are probably in there. The extra half pea, from the dinning table (if not cooked in butter or margarine), shelled and crushed a little so the guppies can get at it, is appreciated. Once in a while give the guppies a little live food or frozen food, first defrosted in cool water and rinse through a fine-meshed net. That will be beneficial.

If you have no water holding containers, buy a couple gallons of "drinking water" from a store. Mostly that water is RO water "rebuilt" with compounds of calcium, magnesium and (for flavor) potassium. That stuff will be ok "for a while" though obviously other elements and trace elements will be missing. As the water is used, refill from the cool tap and treat it with whatever what treatment your LFS (live fish store) felt was appropriate for your tap water. Leave the top off until the water is needed. The day before the partial 25-45% weekly water change (if you have the luxury of that time) try to leave the jugs where they will be as warm as the aquarium. Gradually add the new water after gravel vacuuming the tank over part of the tank bottom.

If you have to medicate the fish (this could well have been done before you purchased it) don't over medicate it. Also, if there are two or more treatments for the same malady, while this is a huge hassle, jot down the ingredients within each treatment and Google those ingredients to find out what the heck they are. If possible, avoid organophosphates, which have been implicated in deaths even of humans.

Oh! And never mix medicines unless instructed to. Talk about a recipe for disaster!

I once lost a fish when suddenly turning on a light in the fishroom about midnight. Out of the corner of my eye I saw a flash of gold and heard a "dunk". The panicked female golden lyretail female had hit the tank end, going full tilt. She was dead.

I sometimes leave a night-light or moon of some sort in the fishroom. It may be an aquarium light over a greenwater culture on the floor. I have one of the little red keyring lights and as I move slowly through the dark fishroom I will use that light, which the fish either don't see or are not so bothered by it.

Sudden convulsions and deaths by fish may also be because of a poison used outside a fish tank in the house. Bug sprays, pest strips cleaning agents like bleach or ammonia, paint strippers, some paints?

Be careful of new rocks, artificial plants or ornaments put into tanks. Are they fish-compatible?

We usually think of tank tops as there to keep fish, water and heat in the aquariums. But they also are there to keep little hands and whatever might be in those little hands out. ;) At any rate aquariums should not be accessible to tots anyway, but make sure that they are as secure as possible.

It would be nice to be able to give you a definitive answer, but I'm not sure even a pathologist, with a lab and dissecting equipment and the fish in hand, within 30 minutes of death, would be able to determine the exact cause of death.

I was out of town when your fish died. I don't think we could have suggested anything other than a partial water change in that tank or, if you have another tank, completely removing that fish out of the tank into water from the other aquarium. Probably it was too far gone to have made a difference.

By the way, you said it had a pointed, clamped tail. Were there tiny spots on the fish, almost like a dust? Did the dust have a goldish or silver hue? Just a wild guess, but if yes, that has implications for the other fish.