yeah sounds like ich if he is itching his sides on everything, crank the temp up to 85-86 and add a tsp/gallon salt for 2 days (to give final of 2tsp/gallon salt) and leave for 2 weeks (if you have to do waterchange then just be sure to replace any salt you take out) also make sure to watch out for parasites during this time, GOOD LUCK
oh and i would suggest rehoming your red belly pacu to someone with a pond, they get way to big for your tank and grow quickly
oh and i would suggest rehoming your red belly pacu to someone with a pond, they get way to big for your tank and grow quickly
But thank you for the advice 
