Just feed them more.
eg: feed them normally and let the neons eat. After the neons have eaten put a little bit more in the tank for the gourami. Let the gourami eat and then remove any uneaten food from the tank.
Don't feed fish as soon as you turn the tank light on. Let the fish wake up and spend an hour or more in light before you feed them. If the gourami is healthy it will feed when it's hungry.
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Stress from tank lights coming on when the room is dark can be an issue. Fish don't have eyelids and don't tolerate going from complete dark to bright light (or vice versa) instantly.
In the morning open the curtains or turn the room light on at least 30 minutes (or more) before turning the tank light on. This will reduce the stress on the fish and they won't go from a dark tank to a bright tank instantly.
At night turn the room light on and then turn the tank light off. Wait at least 30 minutes (or more) before turning the room light out. This allows the fish to settle down for the night instead of going from a brightly lit tank to complete darkness instantly.
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If the gourami is losing weight, it could have intestinal worms or an internal protozoan infection.
Fish with intestinal worms (tapeworm or thread/ round worms) will eat normally but lose weight over time (months). If the fish become heavily infested with intestinal worms the fish can actually become fat and look like a pregnant guppy. Infected fish might do a stringy white poop but not always if they only have a minor case and are fed well.
Internal protozoan infection cause fish to eat a bit but not normally, and lose weight over a week or so. The fish will usually do a stringy white poop and die after a couple of weeks.
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You can treat tapeworm with Praziquantel, and thread/ round worms with Levamisole. You treat once a week for 3-4 weeks to kill any adult worms and baby worms that hatch from eggs. You do a 75% water change and gravel clean the substrate 24-48 hours after treatment.
You cannot use the medications together so you normally treat for one type of worm first and then do the other worms after.
Both of these worming medications are safe for all fish and will not harm plants or filter bacteria.
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Internal protozoan infections are normally treated with Metronidazole (Flagyl). This is an anti-biotic designed for people and should not be used on fish unless they have a known infection that has not responded to normal fish medications.
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I would check your lighting/ feeding regime and feed the fish a bit more or more often throughout the day, and see how they go. If there is still an issue in a week then try deworming the fish.
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As for the clamped fins, this can be caused by poor water quality, protozoan or bacterial infections. Check the fish for white dots; rubbing on objects in the tank; cream, white or grey patches on its body or fins. These symptoms can all indicate a protozoan infection.
Posting a picture of the fish will help us rule out possible infections. Set your camera's resolution to its lowest setting, turn the flash on, and take some pictures. Put them on your computer and find a couple that are nice and clear and well focussed, then put them on here.
Check your tank's water quality for ammonia, nitrite, nitrate & pH and post the results (in numbers) here.