It would be very helpful if you could fill out the emergency template. Here’s the link, pls copy and paste it into your reply and fill out the info the best you can. It’s ok if you don’t have all of the info.
Aquatic Emergency Template | Freshwater Fish Disease and Fish Health Forum | 376562
What else is in the tank and how big is the tank?
What’s your
pH? Sometimes low pH can cause a
liquid test kit to indicate a small amount of ammonia while it’s actually detecting ammonium. Even if this is the case if it ever reads more than 0.25ppm then you need to do a
water change right away. I would recommend dosing with
Seachem prime every 48 hours as a safety net until we get this figured out.
I also recommend you find out what your
nitrate level is, it could be too high and causing stress.
I would add a heater to the tank to keep the temp more stable. Fish can adjust somewhat to in ideal temps but it’s quick fluctuations that tend to be very dangerous even if the temperature is fluctuating within the safe temperature range for the fish. I would recommend you aim to keep the water at around 74F if they are in fact neon tetras. I can’t tell from the photo (sorry if you said what they were and I missed it.
I hope this helps, we may be able to give you more sound advise if we can gather a little more info. For now turning the light off in their tank may also help reduce some stress.