Does the fish normally have the yellow body colour?
I assume that is the Glo part.
Fish get clamped fins from poor water quality, something poisoning them in the water, external protozoan infections or external bacterial infections.
Fish sitting on the bottom with clamped fins can be sick or the temperature might be too cold.
What is the water temperature?
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Protozoan infections will usually cause the fish to rub on objects in the tank. This is in response to the protozoans biting the fish's skin and drinking their blood.
External bacterial infections normally cause the fins to degrade/ rot away very quickly, over a few days to a week.
Your ammonia, nitrite and nitrate appear fine so that is not likely to be an issue.
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This leaves chemicals contamination in the water, or a heater malfunction causing cold water.
Do you use a bucket specifically for the fish tank?
Does anyone smoke, paint, use perfumes, deodorants, air fresheners, etc in the room?
Do you use a disinfectant or perfumed soap to wash your hands?
Do you have any oils, creams, grease or anything else on your hands?
These thing can all poison the fish when you work in the tank or feeding the fish.
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Check your water temperature.
Do a big (75%) water change and gravel clean the substrate each day for a week. This will help dilute anything that might be in the water.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
You can do a big water change every day as long as the new water has a similar chemistry (GH, KH and pH) to the tank water, and it has a similar temperature to the tank water, and as long as the new water is free of chlorine/ chloramine before it's added to the tank.
Make sure you use a clean bucket specifically for the fish, and make sure it hasn't been used for any soaps or chemicals or cleaning products. Same deal with any sponges you use to clean the glass. Make sure they are soap free and have nothing added (like mould inhibitors).
Make sure you don't have anything on your hands/ arms before you work on the tank.
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Clean the filter if it hasn't been done in the last 2 weeks. Wash filter media/ materials in a bucket of tank water and re-use them. Tip the bucket of dirty water on the lawn.
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Bettas are labyrinth fishes and can breath oxygen from the water or air from the atmosphere.