Today, one of my guppies died while I was at work. (I had a morning shift, so I didn't pay close attention to them this morning. I didn't notice any obvious symptoms. There were none last night when I sat staring at them and my triops for a few hours.) When I came home he was swimming weakly upside-down, and I removed him right away to another container, intending to create a makeshift quarantine tank with an old plastic one. When I got back to it with an airstone fifteen minutes later he was gone. (There was no residue on the tank, it had been thoroughly cleaned, and I used tank water.) Upon his death, although none of the others seemed to have anything wrong, I did a 33% water change. (I usually do about 10-15% every other day.)

Now, I am noticing that the gills on my remaining three are shiny (they were not before- it's almost a pearliness that shows up in the light) and the females seem fatter- they were already pregnant, both gave birth shortly after being put in my tank, and all but one fry was eaten. That one is fine, by the way, in a small tank with java moss. No filter but I change about 75% of the water daily with regular tank water. Should I be concerned about my guppies? Or are they just getting bigger as they have more babies growing in them?

[As a side note, I DID just add three small goldfish the other day, temporarily- they were bought as feeders for the turtle by my younger brother but I'm fairly sure they are fancies, and if they are, I have a friend that wants them. If not, I'll give them to my uncle for his pond. They have very unusual patterns. Could the new fish be the culprit?]

:edit:
Last night one of my females went back down to normal size, the other did not.

No, I have my one guppy fry in the separate tank. I currently have three guppies (1-1.5 inch) and three goldfish (1-1.25 inch) in a 10 gallon aquarium with a filter rated for 10-20 gallons. When I do water changes, I add water conditioner to tap water I've let age 3-5 days.

I see . My thought still applies, even though your filter is rated high enough for your guppy tank, the fact that the goldfish are in there, may still create a problem, if the bio isnt adequate to remove the high waste volume created by the goldfish.

So should I do another 33% change today? Do you think that will help? Or should I stay with my every other day schedule and increase the amount I change?

I plan to, I'm just trying to figure out which home they are going to- uncle's pond or friend's tank. If I take them out of my 10 gallon now they'll end up turtle food. =/

I know, it's just my turtle is a brutal monster. He has fun hunting and killing the fish but doesn't always care to eat them after.

I just got home from work- none of my fish look right. I don't think I have a choice other than to put them back in his tank NOW and apologize to the people that wanted them. All three of the goldies seem almost out of it, and my male guppies pearly sheen has spread over half his body. The tail of the fat female looks like it's stressed- the edges are almost fraying. This stinks. =/

Yes, I suppose so. Fish are much more demanding than the other critters I keep. In a way I guess I deserve this for thinking they'd help me prepare. =/

My other male guppy is acting strange now. Do you think a store would be willing to 'babysit' fish while I sort my tank out? =/

maybe?? if you talk to the store manager, and explained.