Tetra with Red Gills in Uncycled Planted Aquarium

[Panda Fish]

So here's the chiz,
I got 8 neon and 8 rummynose tetras in my new uncycled planted aquarium.
One of the 8 tetras has red gills on one side, while the others have slightly red gills which sort of look normal. I can't tell with the rummynose, but they're behaving like normal.
The neons are behaving normal except they hide more often, especially the red gilled one.
Just to be clear, I didn't intentionally get tetras for my uncycled tank. My dad owned a few aquariums a few years ago, and he doesn't believe in the whole "cycling biz" since he never cycled his tanks before but all his fish (except one) did fine. He owned flowerhorns, arwonas, plecos, goldfish ,etc.
I wanted to buy a few guppies to cycle the tank before adding fish, but without my knowledge my dad bought 16 tetras, and put them there. Now, that I'm trying to tell him there's an ammonia spike and I need to change the water. He says that if I do the fish could get stressed and die since the tank is only four days old. He says just let them be, It's natural for one or two to die at first.
What should I do?

 

[Rbishop]

Get a good liquid test kit and monitor for ammonia and nitrites.....do frequent water changes to keep ammonia at less than .25 ppm....

 

[tanker]

1) Get a test kit and check for Ammonia, Nitrite, and Nitrate.
2) Do some water changes (you are using a water conditioner, right??)
3) It is not normal for some fish to die first.
4) When you say planted tank--, how many plants and what kind??

 

[ROYWS3]

If it's HEAVILY planted and the plants have been in there long enough for themselves to be established and to have started growing, your fish may have a chance. Most plants consume ammonia first as their nitrogen source as it is the easiest form of N for them to metabolize, but like I said they would have to be growing - not just recently added.

Do a lot of small water changes with conditioned water

 

[Panda Fish]

I do use water conditioner, and I have 2 water sprites, a few amazons, java moss and some type of fern. The plants have been there for less than a week before my dad added the fish. I think I will start changing the water. I will purchase test kits soon. They're a bit harder to get here in the Philippines. Thanks

 

[Panda Fish]

So, I just changed the water in my tank. The one that was doing the worst died while I was changing the water. One neon is missing, probably hiding. One neon is really stressed out and won't eat. The rest of the neons are doing fine, hiding more often, but fine. The rummynose tetras seem unaffected.

 

[Panda Fish]

So the really stressed out neon died as well, and I think it was because of the water change because they both were sick then stressed by the water change. Therefore sick + stressed = die. Is there anything I can do to make the water change less stressful?

 

[ROYWS3]

SO How big is the tank and how big are the water changes?

 

[authmal]

I do use water conditioner, and I have 2 water sprites, a few amazons, java moss and some type of fern. The plants have been there for less than a week before my dad added the fish. I think I will start changing the water. I will purchase test kits soon. They're a bit harder to get here in the Philippines. Thanks

In store, it may be, but you have internet access, so you have access to places like Amazon, where an API Freshwater Master Test Kit is something like 25 USD.

And, unless you're doing something really weird or really wrong, water changes aren't really stressful for fish. What is your process, from beginning to end?