my tank has been stable for week or so, and i decided to add some guppies. added five females from two different fish stores. i tested the water and it was still good after that. no ammonia.. no nitrites... nitrates good. now the females are dying. there are two that are doing ok.. two have died... one dropped some fry before she did... and one isn't looking good. the temp is at 78 ... is there anything special guppies need? i remember guppies being hearty fish but they don't seem to handle the move from the LFS to my tank. i acclimate them properly. any suggestions?