pregnat guppies

[Bren]

Hi, I have two female guppies left in my tank with 2 corys, 2 neons, 2 ? black with gold stripe tetras ( were in the guppy tank with guppys when i bought them at the pet store) and a large algie eater. My tank readings are good according to lady at pet store: pH7.6, Amonia 0, nitries0.1, Nitrates 0.3, KH 70, GH 160. I have to go away for the weekend, but someone will be home to feed my fishies. I think my females are ready to give birth as they have been pooping all day. their bellys are very rounded and the g spot on both gets very very dark at times, darker and fuller than ever. I do not have a fry tank but it is a 10 gallon tank with lots of plants for fry to hide. My question is isthere a way to tell if they will give birth while I am away this weekend. We had a batch of fry a while back but they dies and so did my other fish as i was told to feed the fish lots so the fry would not get eatten. Well I did that and the fry did not get eaten but my Nitrite, Nitrat and Amonia levels went throught the roof. I think that is what killed almost all of my other fish. My children were devistated. I replaced them with the ones I have now and everything has been good since, so this time I am not overfeeding them, when the fry come. Thanks Bren