so I just checked in a conversion thing - between 15 and 16 gallons.
With 27 guppies in there, while they are a relatively small fish is overstocked. In a 15 gallon you would really only have space for like 10 :/
Having that many can easily make the water parameters out of whack which could be why you are seeing some issues.
if you can I would take some back. They are also prolific breeders so you will get fry eventually too. It can get out of control pretty quickly.
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