They may be pond snails, or bladder snails, but either way they lay eggs in little blobs of jelly that are hard to see. So you may see more snails, despite cleaning the tank as you did. If so, just take them out when you see them.
If you want a steady supply for the loach, give the snails a clean tank, as they prefer clean water and plenty of oxygen. They are hermaphrodites, so they can reproduce with or without a mate, but they prefer with a mate, it gives them a survival advantage.
Feed them fish flakes or a bit of algae tab. If they have not eaten it all by next day, feed less, so as not to foul the water. They also eat dead plant matter. If happy and well fed they can reproduce quite quickly, but if you let their tank get dirty, it will slow them down. They can survive in bad water for awhile, but do much better if it is clean.
I keep ramshorns, MTS, mystery and Poso, or Rabbit snails. They all do a lot better in tanks that are clean and well filtered, just like fish or shrimp.