Breeder guppies dying

[Vaelin]

I had 7 guppies for breeding, 4 female and 3 males. I've had them for over a month and no breeding has happened and in the past week i've lost all but 2 of them.
The only problem is, all of the levels of nitrates, ph, ammonia, EVERYTHING is perfect, literally as close to spot on as I could make them. The temp is somewhere between 79-81 degrees.
The fish didn't show any signs of distress before the dropped dead, nor is there any sign of any parsites, fungus, ick, or anything. The water is crytal clear, no odd smells or anything.

I'm not entirely sure whats going on with them..I'm hoping I don't lose the last two. Could it just be that they were unhealthy (from petsmart) when I got them? but in that case i've had them for over a month and they just now died..

I know it's hard to diagnose without any symptoms at all but...does anyone have any ideas?

 

[Kaosu]

how big is your tank?
how long as it been up?

 

[knifegill]

What did you deworm them with? Try Prazi-Pro instead. Always cleans up my feeder stocks!

 

[Vaelin]

I put them in a 10 gallon for the first month and I was going to move them to a thirty gallon until they started dying off. the tank had ben up for a couple weeks before that.

knifegill- Is that available at most pet stores? I havent seen anything called that up here, but then again I havent looked for it so thats probably why. I'll check it out