from what I have seen the fish is interested in food but doesn't appear to swallow the food
This is a classic internal parasite symptom - so much so that without a (microscopic) diagnosis, it's where I'd start treatment
I've fed frozen bloodworm, brine shrimp, daphnia etc for years & have yet to experience any negative effect, I do feed Hikari (good sterilization process of all their frozen foods) & buy from shops with exemplary freezers (care of frozen foods) & store at home in a (manual defrost) chest freezer rather than a fridge freezer (seldom as cold & most run auto-defrost cycles)
The levamisole is much more effective/broad spectrum than metroplex & less resistance than observed with flubendazole
Begin with a 2mg/litre dosage (more effective at pH less than 7.2), you can slowly increase this to 10mg/l BUT I'd not subject shrimp etc to this - depending on fish species, they may appear unaffected or quite stressed by the levamisole bath
As with metroplex, switch to levamisole-soaked food for (much) better efficacy
Again soak for only 10min, it is less palatable than metroplex~food, again Focus will assist with binding (also seems to improve palatability)
Treat 3-5 days "On"
Then 5-7 days "Off" but restart medicated food sooner if symptoms persist/return
Treat 3-4 days
Monitor tank for next 1-2 weeks, a third treatment is unlikely unless there is a disease source in the tank
- but depending on the disease agent, a repeat treatment at 3 & 6 months after the last medicated food cycle, may be beneficial
If buying the linked bird medication (unbelievable this is available without a script when Metroplex is not
), it seems to be 80mg/ml so nicely concentrated allowing you to avoid introducing high levels of other components in the mix - hopefully bottle has an ingredient list
Contains levamisole hydrochloride 8%w/v (80mg/ml).
80mg/ml x 3ml ~ 240mg in 100 litre tank volume ~ 2.4mg/ml
The dosage instructions for medication use in fish tanks is always done with bare tanks as the reference, so err on the side of slightly more rather than less - some percentage of the active ingredient will always be impacted by various tank factors (dissolved in water column, sequestered by filter, substrate etc)
Ideally,
Day 1 - 25% water change, add 3ml
Day 2 - repeat water change & dose 3ml
Day 3 - repeat water change & dose 3ml
NOTE - if fish still shedding & not eating, continue this water change & dose for Day 4, 5, 6, 7
After Day 7, continue as indicated below regardless of symptoms
Then restart the Cycle after the 72 hours of running carbon
(though if this is necessary I'd find another levamisole source, it should not be this ineffective unless there is some dosing issue, easiest is replace with a different lot # medication if possible, or purchase from a vet etc where you can see how the medication is stored - a major issue with online medicated compound sales regardless of market or drug, there are also black (?) market versions of drugs that are very well done "fakes")
Day 4 - 50% water change, run good quality activated carbon (Seachem etc for Reef tanks is much better binding than most sold for freshwater)
Day 5 - 7 25% water changes (this a standard disease treatment protocol)
Remove carbon after 72hours & dispose (note you won't need much reef carbon, maybe 10-20g to treat100l)
If fish seem back to normal, feed mediated food for 3 days, beginning 2 weeks after last levamisole dose (ie Day 17 or 18 ... 2 weeks is long enough for most parasite egg stages to begin hatching etc, not enough time for most parasites to restablish in numbers & mature to egg production stage)
The stringy white feces is intestinal shed - an effort by the host to remove/dislodge parasite from the intestinal tract, this usually contains some numbers of parasites (& possibly multistage) hence the daily water change & bottom syphoning of bare treatment tanks, all glass surfaces would also to wiped down daily