5 Gallon Tank Help! Is this guppy dying?

Tank
5 gallon, 3 days running water, then 3 new guppies introduced, today's day 9 (yeah.. not cycled).
Have a small filter, no heater, water temp 75-76F
aforementioned 3 guppies +

Maintenance
partial (15%) WC's on day 4 and day 6
Initial water was treated with Stability
When WC, I put prime and Stability
Vacuumed substrates

*Parameters - Very Important
Apparently, not cycled.
Used API test strip (5-in-1). Didn't check the ammonia.
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: ?
Nitrite: 0
Nitrate: 0
pH: 7.0-7.5

Feeding
twice a day (morning/evening at 8), a small Tetra Min flake, a size of half a centimeter or less than a quarter inch diameter.

Illness & Symptoms
-it was pretty normal and active during the first few days
-became wiggly after putting a stem of hornwort on last Thursday; been shimmying for the past 4 days, with clamped fins; a small reddish spot (that looks like a bleeding) at the top fin.
-did partial WC as mentioned earlier; the other two seemed happier and much more active after WC, but the sick one did not show much change.
-no physical injury or illness upon purchase

Now it's just floating around the corner, without moving or eating at all, except for when the other two guppies bother him sometimes.
I was afraid of doing anything other than WC to increase the stress level, but by now he seems to have lost strength, his mouth is closed tight, and I am not sure if he's past saving...
Would any medicine or cure help him to revive?

I'm attaching the link to his video since the photo doesn't show him well.

 

Since tanks not cycled recommend larger water changes. Can't tell what's wrong from the video but I'd add aquarium salt just to be careful.

 

If this japan blue guppy will die is something that can not be told directly. I would add some salt to the water. And a small water change.
I love japan blue doublesword guppies...

 

He eventually passed away...
but at least I was able to save another fish that got the same symptom.
Thanks for your suggestions!

 

You are going to have to keep up with water changes, pretty frequently until the tank is cycled. You have ammonia in it, that is certain. All waste decomposes into ammonia, and it is constantly being produced in any aquarium. The cycle is what eliminates it. Any amount of ammonia can be toxic. You should/could add some prime, or other product to detoxify the ammonia until your cycle gets going. Good luck with the other fish, but track it carefully, change the water frequently and detoxify or you will lose him too!
Sorry, just read you are using prime. The other thing that comes to my mind is that they are oxygen starved. Add an airstone or flow to the tank. Low oxygen can come from high levels of ammonia in the tank, and those fish are showing all the symptoms. Labored breathing and gasping for air at the surface. Good luck.

 

He eventually passed away...
but at least I was able to save another fish that got the same symptom.
Thanks for your suggestions!

Sorry to hear...