whats up with my guppies

Question
ok i have 4 male guppies and 8 female, 3 weeks ago 2 had fry so i know my tanks healthy, but 2 of the females wont get pregnant. These are 2 different females than the ones who gave birth. Is something wrong with them or are they just duds?

Answer
Hi Lizzy;

They may be too old or too young to breed or they are simply sterile. Sterility can be genetic, from underlying disease, malnutrition, water quality problems, etc. Keep your aquarium very clean by changing 25% of the water at least once a week. Give them healthy foods such as frozen or freeze-dried brine shrimp, worms, daphnia and spirulina algae to get them conditioned. Even if the two still don't have babies they will all be healthier in the long run. Good luck!

At Your Service;
Chris Robbins