Are you seeing any white fecal casings, often stringy or mucus-like, can mean stress, diet issues, or a healthy mucus lining, but when accompanied by symptoms like bloating, not eating, or wasting, they often signal internal parasites (like Hexamita/Spironucleus). There are different ways to treat. In general ingesting the medication is by far the most effective.
#1 You could try something like bloodworms coated with Seachem Focus and metronidazole just to see if the fish will eat fed daily for 7-10 days.
#2 If it still refuses food then you could try treating the entire water column, start with one gram of metronidazole per 20g daily for 10 straight days(100g would be 5 grams). I do daily water changes prior to dosing as metro doesn’t have a long shelf life dissolved in water.
#3 I have also had great success injecting 12mg metronidazole with a little water to squirt directly into the gut with a plastic pipette doing this daily for 7 days for 7-10 days. Take the fish out and place on a damp towel and slowly insert the pipette into their stomach(this is more stressful for the fish and yourself).
#4 I have no personal experience but RD has this as a sticky in the health forum.
https://www.monsterfishkeepers.com/forums/threads/treating-hexamita-aka-spironucleus.523470/
These are the pipettes I use.
I get metro in bulk from Jack Wattley discus.
Metronidazole is Very effective in the fight against protozoan, hole in the head disease, internal hexamita (Malawi bloat), freshwater ICH and pond epistyles.
wattleydiscus.com
Once finished ultimately you’ll need to address the cause to prevent future occurrences.