Bizarre yoyo loach behavior

[CluelessCritter]

About three weeks ago I bought two Yoyo loaches since I had been looking for them and they were the only ones left. They seemed fine at first, but when I tried to reintroduce a fish into the tank, one of them started going out of its way to attack it. Even after I took the fish back out, that loach keeps harassing other fish in the tank. What’s weirder is that it tends to flip itself upside down after nipping a fish and sometimes swims upside down or sideways around the plants and wood. The other Yoyo loach seems fine, and it’s also being picked on by this loach. I’m new to loach keeping so I don’t know what to do. Here’s a few details about my tank that might be the reason why my loach is doing this:
I haven’t been able to find more Yoyo loaches in my area, so it’s just been those two
My tank is a 20 gallon, I’ve heard you can put yoyo loaches in a tank this size but I’ve also heard the minimum should be 40 so maybe the tank is too small
In the tank, there’s the two yoyo loaches, a baby bristlenose, kuhli loaches, shrimp, and a betta fish (despite being a male betta, he’s always been peaceful)
I have a mix of gravel and sand for my substrate and I heard loaches don’t like gravel, but my kuhli loaches seem fine with it.
I just redid the tank, so the plants haven’t really spread out to provide hiding spaces, but there’s still hiding places.
Sorry if this is long and hard to follow, this is my first post.

 

[Colin_T]

Need a video of the fish
You can upload videos to YouTube, then copy & paste the link here.
If you use a mobile phone to film the fish, hold the phone horizontally (landscape mode) so the footage fills the entire screen and doesn't have black bars on either side.

Yoyo loaches (Botia lohachata) need to be in groups of at least 6, and 10 or more is preferable. They have a pecking order with a dominant female ruling the group. If you only have 2 fish, they are probably fighting over who is going to be boss. The aggression towards other fish is probably due to the low numbers of loaches.

 

[powerdyne6]

I agree with the above

Yoyo loaches need to be in bigger groups. I have 10 in my 75 gallon and I have seen 0 aggression in the 5 or so months I have had them. I keep them with 20 Tetras. They also need a soft sand substrate.

They also have some very odd behaviours.. they swim upside down along the leaves of the plants and branches on the wood. I have also seen them sleeping upside down on the sand or on their sides.