Your KH and GH are low for guppies I would add some crushed coral in a media bag to your filter or you can mix it into your substrate to help increase your GH and KH what I would do if you can is quarantine the guppy with the lumps on it's fins and treat with aquarium salt 1 table spoon for 2 gallons for weeks it could be lymphocystis that a viral infections there no treatment