This happens sometimes. I've had amazon swords do that before.
But something to be mindful of, when I read the reviews for your carpet grass, people were saying the root system of the carpet grass overtakes and smothers other plants' root systems. Some reviewers say they ended up ripping the grass out so they could keep other plants.
I have to agree with Colin, here, though. You have no hiding places in the tank, and that's stressing the loach out. That's why it tries to hide under the air stone.
Byron mentioned your susbrate could cause issue for bottom dwellers, like corys or loaches. I don't know much about your substrate brand, but I do trust Byron's judgement.
It's starting to look like redoing your aquascape is in order. My suggestion:
Rip up the mystery grass. Pour a layer of play sand from the hardware store on top of your gravel. Then add new plants. Replace the mystery grass with dwarf hairgrass or java moss. Add some "stuff" to the tank as well, like large rocks, caves, driftwood, whatever... just provide lots of hiding places for the fish. I know it sounds weird, but the more hiding places you provide, the more you will see your fish, as they will be more comfortable and feel more secure. Tall plants help with this too, like amazon swords or mature java ferns. You don't have to go nuts, but your tank is just barren right now. Imagine that fish tank is your apartment. It has no furniture. It's just an empty room with a plant in the corner. Wouldn't you be more comfortable in an apartment that has a sofa and a bed and a dining table than you would in an empty apartment with a plant in the corner? Imagine having roommates in an apartment with no rooms/walls. You can essentially create "rooms" in the tank by using caves and plants and other decor. If you're not confident in your ability to keep plants, that's okay, opt for more driftwood/rock/cave decor. Clay pots work great for creating caves, even cracked ones, and are much more affordable than a plastic shipwreck or from the pet store.