Something Wrong With Kuhli Loach?

Hello all I haven't listened here in a long long time as I've been busy as heck with other stuff. Anyways, one of my KuhlI loaches is displaying some odd behavior and I'm not sure if it's illness or something.

PICS + VIDEOS AT BOTTOM

I'm worried because a few weeks ago, two KuhlI loaches that I've had for about six months died within a few days of each other with no apparent COD. I'm worried about this KuhlI now too.

I'm not sure how to sex KuhlI loaches so I have no way of knowing if this is a gravid female, or anything like that.

SYMPTOMS:
-Swimming erratically around the tank at high speed and glass surfing.
-Strange, dark/silver-ish colouration
-Strange body shape, belly looks distended and has a boxy kind of shape.
-Short bouts of what looks like hyperventilation (breathing super fast) and then appearing to stop breathing.

TANK PARAMETERS:
-Temperature is at a constant 25°C
-Moderatley planted tank, with sand substrate.
-Lots of hiding places between rocks, and a large cave for bottom dwellers to hide in.
-No CO2
-Ammonia is 0ppm
-Nitrite is 0ppm
-Nitrate is ≈20ppm
-pH is 7.8 (it is also 7.8/7.9 in my LFS; I have kept these particular loaches for 8 months with no problems. I originally had 13, but after the two unexplained deaths I now have 11.

I'd love any help/replies and any knowledge at this stage is super helpful!

Here's a video and some pictures I took during a water change:

 

UPDATE: how do I upload a video?

 

UPDATE: how do I upload a video?

You need to upload to YouTube then link to it

 

You need to upload to YouTube then link to it

Thank you!

 

I don't know what could be wrong with your loach, but he/she looks like hes/she's in pain or being scared to death by something! I hope you figure out what's wrong and he/she gets better soon!

 

Glass surfing is usual in kuhlI loaches mine do it every time I do a water change or get new plants.

The thing that looks odd is the pink around the gills and tail. This can be a sign of ammonia poisoning although you are testing 0 idk what it could be