Do you want the guppy fry to live?
Yes...
Smaller fish such as Otos, perhaps bottom dwelling dwarf Cichlids such as Checkerboards, or Sparkling Gouramis. A school of Dwarf Cories could work, too.
Guppies have been bred in captivity until many will handle the softer water that many small fish like, but if you are getting a strain that needs harder water...
Pseudomugil furcatus and related fish are good in harder water.
Many Cories do not mind it, either. Check the optimum parameters, though, some are more picky.
If you do not mind the Guppy fry becoming a living food source, then slightly larger fish could work. Most Rainbow Fish will thrive in harder water, perhaps a mid-sized species like Melanotaenia machullochi would work.