My daughter got a pregnant guppy three days ago. She (guppie) does not seem to be eating. Sometimes she seems to be dead and floating on the top of the tank. Then all of a sudden she swims away fast. Please tell me what this could mean. I have added salt to the tank, as advised by the pet store. My pH is good and when we got the fish the pet store tested the water and everything was good...Please help us.