PrairieSunflower
Fish Gatherer
For the best health of your guppies, it would be good if you considered upgrading to a 10 gallon tank and did a fishless cycle (see the beginners section for a how to), or you could seed a new filter in a bigger tank with mature media (another good question to ask on the beginners forum.
A bigger tank that is properly cycled will help keep your water stats stable and will reduce the likelihood that your fish will fall ill (poor water quality makes your fish susceptible to more illnesses).
A bigger tank that is properly cycled will help keep your water stats stable and will reduce the likelihood that your fish will fall ill (poor water quality makes your fish susceptible to more illnesses).