Can we get a picture of the entire tank?
What is the ammonia, nitrite, nitrate, pH and GH of the tank water?
What is the pH and GH of the shop's water (where you got the fish from)?
What was the shop feeding them?
How long had the fish been at the shop for before you got them?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the tank?
How often and how do you clean the filter?
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Stringy white poop can be from intestinal worms, internal bacterial infections, or an internal protozoan infection.
It's unlikely to be bacterial because that usually causes the fish to bloat up overnight and die within 24-48 hours of bloating.
It's possible the fish have intestinal worms.
It could have an internal protozoan infection, which causes fish to stop eating or reduce the amount of food they eat, and die over a week or so. If you have had the fish for a couple of weeks (and they should spend at least 2 weeks in quarantine), then it's unlikely to be an internal protozoan infection.
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Quarantine tanks should have a thin layer of substrate to reduce stress and stop the fish being able to see their reflection on the bottom. The tank should also have a picture or something on the back of the tank to make the fish feel more secure. And there should be caves or plants (real or artificial) to provide hiding places and make the fish feel more secure.
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Try feeding live or frozen food and see if they eat that. A lot of people that breed cichlids (in particular rams), use frozen and live foods and the fish usually ignore dry foods. Rams also don't eat much if any plant matter. They like insect larvae, worms, small fish and shrimp.
I would try frozen (but defrosted) brineshrimp, daphnia, bloodworms, marine mix (prawn, fish & squid), and raw or cooked prawn/ shrimp. If you have live shrimp in the tank, use cooked prawn.
If the fish don't eat live or frozen foods, and the pH and GH are correct for the species, they might have an internal protozoan infection. However, I would try different food and see what happens. Then if you want to treat them for anything, treat them for intestinal worms.
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Depending on tank size, the dwarf gourami might be ok if you have lots of floating plants. Water Sprite (Ceratopteris thallictroides/ cornuta) is a great plant for dwarf gouramis and the plant can float on the surface or be planted in the substrate. It grows rapidly so you only need a couple of plants and before long there should be plenty of hiding spaces to make the gourami feel happy. If the gourami continues to attack fish after that, then get rid of it.