Empty Snail Shells?

I recently bought five mystery snails and added them to my tank with my 2 Rosy barb females(originally 5), two sucker catfish, 4 red wagtail Platys, five guppies and one black swordtail male. They were fine for about a week but in the last couple of days I’ve found all of my snails at the bottom of the tank with their shells empty except for one which is absolutely fine and still roaming around the tank and eating. I’m not sure what fish is attacking them and eating them? And it must be happening at night.

 

The "sucker catfish" is probably the culprit, but it's very possible they died and were eaten afterwards.
What do you mean by "sucker catfish"? I assume some type of pleco, what type do you have?
You can post a picture if you don't know, people are really good at IDing here

 

Yes not sure what they are called they were sold just as “sucker catfish” here is a photo.

 

That almost looks like a Siamese algae eater, but I'm not sure about that.
I think it is likely some type of loach, and those guys are known for eating snails. How large is it?

 

The snails were about 2cms and the catfish are about 5cms


And apparently they grow to 60cm

 

Okay, I'll have to wait on someone else to come along and give a positive ID, but the Rosy barbs, platys, guppy's and swordtails are unlikely to be the culprits

 

What are you feeding the snails? I bet they are dying because you aren't feeding them properly which then let's the other fish eat the dead snail.

 

That is a Chinese Algae Eater. Not a Siamese. It will most likely get aggressive to other fish as it grows. What size tank do you have all of these fish in? I don't think snails are being eaten, but could be dying of another cause.

Edit: Is this all the the 42 liter tank? (11g)

 

What are you feeding the snails? I bet they are dying because you aren't feeding them properly which then let's the other fish eat the dead snail.

Yes it’s in the 42L tank and I am feeding them pellets not sure if they are eating them

 

Is this an established tank? Is there algae growing for the snails to eat? Plants? Is the tank cycled? You are overstocked and if you are getting an imbalance in your cycle you may be seeing the signs of it through your snails.