[ramonesfreak]

swim bladder issues do not typically come and go in the pattern you have described

and they are typically caused by injury —-there are many causes though

But if your fish had a swim blade problem he would be floating uncontrollably all the time

this usually leads to death rather quickly…weeks

but as i said above, especially with a turtle(s), water changes once per month are not enough….though i admit i have not seen your filtration system

and even if using well water, i would recommend always using Seachem Prime when doing water changes

all my tanks have one additional filter. i over filter and always change once per week. you should at least do every other week

my tanks also have real plants which contribute to filtration…..don’t bring plants in from pond or lake or you will have dragon fly nymphs and planaria all over the place…been there done that