I don't know what that is. I'm not familiar with aquarium salt. I got a litle box of API "Aquarium Salt" and I've just had it in a little container. Doing very little in there.
It's fine, it just isn't going to do anything for the bloating. Ideally if they're eating you should dissolve a small amount of epsom salt in some tank water and soak their food in it. And also dose the water with epsom salt, maybe a teaspoon a gallon.
You should always assume young spiny eels have internal parasites, as almost all are wild caught and it's common. They are also often kept in poor conditions when imported. I would treat for internal parasites with this Epsom salt food soak as soon as I got the fish--with any young eel, or older if you suspect it.
"Aquarium salt" is perhaps one of the biggest rip-offs in the entire hobby. API is laughing all the way to the bank at people buying their "special" salt.
If yes on both salts, then is it okay that my loaches eat it too? There isn't much I can get to the eels without the hoard quickly rolling in to investigate.
Yes to the first question, no to the second. It's called Epsom salt... You find it in a drug store.
You can also throw it in your bath tub and soak with it (great for sore muscles) and use it as a laxative (haven't tried this one haha) if you dissolve it in liquid and drink it.
For fish, it has long been known to act as a mild laxative when in the water column, but recently studies have pointed to great results at eliminating internal parasites when ingested. This is why I suggested the food soak.