Guppies can live in a wide variety of water temperatures and water
conditions. This does not mean you can put your fish in an abusive
environment and they will thrive though. However, they can live through
short periods of unclean water.
Guppies can live happily in temperatures from 60 to 90 degrees F (15-30
degrees C) but are happiest in the mid 70s (low to mid 20s C). Although
they are fresh water fish they do well with a little bit of salt, about 1
tablespoon for every 5 gallons of water. The pH of the water is best
between 7.0 and 8.5.
Since guppies are smaller fish they really like live plants in their
aquariums. The live plants will provide shelter for their babies and a
home for any live food which will feed them (microscopic organisms).
A gallon or two of water is recommend for each fish, so a 10 gallon tank
should not hold more then 10 adult guppies. With filtration and water
changes you can have more.
Water changes are needed for guppies, like with all fish. Changing the
water will remove chemicals which your filter or plants can not get rid of
which will end up poisoning your fish. Since guppies are small they
produce less waste then larger fish, but a 10% water change per week is
recommended to keep your fish healthy.