It's either unhealthy stock or unsuitable water condition. Can't help it if it's from unhealthy stock but can't be blame also. Ancestral guppies aka the longkang guppy are quite hardy that's why in some longkang with terrible condition it still thrives. However the aquarium guppy is known more as Fancy Guppy which breed through the years to amplify the colours and features of the guppy. The creation of fancy guppy was through numerous line breeding or loosely known as inbreeding had some major setbacks. Most noticeable is the immune system. Fancy guppy nowadays have very low immune system because of the linebreeding method and also the perfect conditions it was bred in. Therefore, most fancy guppy nowadays require almost the identical conditions which it was produced. Even for experienced breeder (ahem not me) a sudden wipeout/deaths are unaviodable. So please don't be surprise because I've known there are even more diff. species to handle than guppies. (I myself already had about 20 deaths total from last month till now-sometimes it can be frustrating lucklily compensated by about 30 fries and 3 adult left). Well for RM 1 apiece the LFS guppy is quite cheap. In this forum you might have noticed some of the sifus paid top dollars up to few hundred for a pair. Even in KL the standard LFS guppy costs about RM1.50 apiece. So Happy Guppying!!!!