If your aquarium persistent at a pH of 4.33 no matter what, it is possible that Escherichia Coli has taken hold,
Escherichia coli Infections 160 410 730 830 7500 (sq 3560 3930 4250 6105 8260-7) Hz
and repeated here a set of frequencies to kill off common algae on the walls of the tank,
Parasites Stigeoclonium (algae) 680 900 2500 5500 (sq 1393 9350 4042-5 4152-5 4120 4070) Hz
Guppies are more difficult than goldfishes.
Good night.