Do you have salt in your tank? If you do use salt...try raising them without salt.

Guppies that you purchase in pet stores are usually older....that may be another problem.

What is the hardness of your water? Guppies also do better in harder water.

Also your quarantine tank/hospital tank should be empty......that is the point.......when bringing in new fish so they don't pass on disease and parasites to your existing fish.

Good luck.
Sierra

Same here and got mine from petland, they had to destroy tank they came from. I am treating two remaining males (gave others away) who have curved spines (one sideways other arched) which indicates inbreeding, not being fed properly when young so on... Now treating for fin tail rot... heard another person while at same store said all the guppies he got from new arrivals have died. I had to treat all the fish from there for ick, four times, which stressed the cories and one died... Now two tanks seem to be doing ok, babies from previous guppy moms who later had to be put down, are doing ok, but don't look as fancy thats for sure.... water in NYC not so great as well... all readings normal... have added salt but not too much as have cories who are sensitive... from what I have read, as sierra mentions old by the time you get them, best are sold elsewhere, and much inbreeding over the decades and worsening water world wide due to heavy metals so on, makes them less hardy then when we were younger.... they were very hard then as I recall... now seem to be my least hardy..

Best Sherry

i had hard water where i used to live and couldn't keep guppies, even the ones purchased from breeders at auctions. if you go to breeders, you will pay a higher price.

Here is a link that might be useful: see if this helps...

I have soft water and my guppies thrived, both here in the fresh water tank at work. In fact, all they did was produce fry after fry. When the spine starts to curve on fish, that's a sign of TB. That's not good!

linda, please explain TB.

thanks!