hi, quite sometimes not here. I just like to advice you not to use hanging type water filter in guppy tank, especilly those size within 1 to 2ft. I'd recommend you to use sponge filter or undergravel filter, this work more effectively in guppy tank.

Regarding your sick guppy.. I'm sorry. I believe your fish is stressed, probably b'coz of deliver them into new tank which water condition totally so much different with the previous tank. It could be temperature, pH, kH, etc. It is hard to cure when the fish turn to that situation. See ur luck.