I used to have the same low pH problem when I grew my pacu up when I started fishkeeping in the early 90's.
pacu grew to 18" long and ate like a pig.
tank was only 65 gallons.
high ammonia in the tank, pH low so the ammonia was non toxic, that was the only reason the pacu lived. I sold him as I could not keep the water quality in check even with regular water changes.
there is really little your going to be able to do as a long term solution for this problem.
your fish need a pond.
a tank is not going to cut it.
if you cannot house them properly please find them a new home immediately before they die. thats what I had to do.
in the meantime big water changes and feed every other day (to help keep waste levels down - they are not going to starve) is about all you can do.
good luck
pacu grew to 18" long and ate like a pig.
tank was only 65 gallons.
high ammonia in the tank, pH low so the ammonia was non toxic, that was the only reason the pacu lived. I sold him as I could not keep the water quality in check even with regular water changes.
there is really little your going to be able to do as a long term solution for this problem.
your fish need a pond.
a tank is not going to cut it.
if you cannot house them properly please find them a new home immediately before they die. thats what I had to do.
in the meantime big water changes and feed every other day (to help keep waste levels down - they are not going to starve) is about all you can do.
good luck