why do seeming healthy fish just die overnight?

[zola11]

in the past 4 weeks i have lost 2 platys,2 mollies, & 2 swordtails, have checked parameters n all ok....1 mollie seemed to start losing weight slowly but was eating well and not  stagnant at the bottom, as i say the others showed no signs--is it old age and if your times up its up!
we bought them all from lfs so have no idea of age but mollies were a good size.
thanks in advance

[TropicalFishForums]

[ClothahumpDisabled]

When you say "a good size" what exactly would that be?

[chrisjj]

Tank Age?
Tank size?
Water test results?
Which lfs?

[zola11]

When you say "a good size" what exactly would that be?

maybe just over 2.5in-nice full looking bellys-apart from the one that started losing the weight..(skinny disease?)

Tank Age?....1 year
Tank size?....100 litres
Water test results?...amonia 0.1mg/l   nitrite0.0mg/l   nitrate 0mg/l  ph 8.5
Which lfs? a local one in essex-not pets at home etc but a properly run family shop

 other fish in tank are
 2 3in clown loaches,3 guppys,2 zebras,3 neons,3mollies,2platys 1 flash pleco,
 1 sailfin leopard pleco(3in)

[plankton]

Had you had the mollies and swordtails for a year? If so, it does sound like old age, and the "skinny" one, was that a female perchance?

(BTW, the tank isn't big enough to raise clown loaches properly, and they should be kept in bigger groups)

[zola11]

 yup swordtails were full size when bought,and the mollie was a female-had given birth to a few "litters" i had read that 2-3 years is about average for most of the livebearers-we have had the mollies for a year and they were not small then ...

[plankton]

Most livebearers that get sold are about a year old. Anything over 2 years is a bonus really, so it sounds about their time unfortunately

[stonec0ld]

The Molly I bought died after about 18 months, the offspring I have left is about a year old and not yet at the size the original one was when I bought it so I'd agree with plankton