Before I start, I currently reside in India, where meds like Prazipro and Paracleanse aren't available in the local market, and can only be imported into the country at exorbitant costs. Hence, my decision to proceed with the steps outlined below.
I have a group of 5 juvenile angelfish which came from the store with internal parasites cause they all were passing white, stringy faeces, in a 40 gallon tank. I put them through a 10 day course of treatment with food soaked in 400mg metronidazole once a day with 40-50% water changes after 8 hrs and they did eat the food but 2 out of the 5 didn't get better.
The following week I noticed the 2 outliers not doing too good and just hanging at the top of the water, not showing any interest in food or anything, and they did have white, stringy faeces again. The other 3 were eating fine and doing great. Since they shared the same tank, I decided to treat them again with metro soaked food in the hopes that it would help the ones that were eating as well.
This time, I used 800mg of metro instead of 400mg like last time. Around 6 days into the treatment, I noticed that all 5 of them stopped eating any of the food, and so I stopped the treatment with the 7th day. It's been over 2 weeks since then, but none of them has eaten any food since then (as per what I've noticed).
Also, I have a couple of Ramirezi, some juvenile Red Head Tapajos I'm growing out and a large male Bristlenose pleco in the same tank who all went through both treatments and are doing more than great, pigging out during feeding time.
All 5 Angelfish are currently very active, have great finnage and are swimming throughout the aquarium, squabbling with each other and even coming up to the top of the water when I approach to feed them. But they show zero interest in the food, sometimes mouthing a piece and spitting it out immediately and then swimming away. I can see that their stomachs have sunken in as well.
Looking for any help and advice to get them to start eating again. And on the subsequent treatment required. I'm currently on day 3 of trying to get them to eat food soaked in Garlic Guard but no luck yet.