Disappearing Cardinals?????

Yesterday I bought 7 cardinal tetras. Today I have 2.

They were put in a well established 55 gallon with some guppies, 4 small fancy plecos (all under 3", most under 2") and 2 queen loaches (i know, too few, but they came with the tank and I haven't found more). The tank has lots of rocks, caves, drift wood, some plants. They aren't in any of these things. I scoured the gravel, no cardinal corpses. I fed cucumber last night, so there is no way the plecos had time/room to eat 5 whole cardinals.

The tank is filtered by a fluval 305. I took it apart and checked inside, no cardinals, no cardinal corpses or body pieces.

There is some space in the tank hood where I suppose they could have jumped (!?!?!?!?) but the water line is fairly low, they would've had to have jumped an inch or more above the water to get over the rim. I don't think they are capable of jumping that far, and they certainly seemed happy in the tank when I went to bed last night. The tank is wedged between furniture, there is no way to check the floor for jumpers without tearing the whole tank down.

I'm so confused. Any thoughts? Has this happened to anyone before? (I'm so shopping for sponge filters and glass tops right now... sigh) The two remaining cardinals look so sad and lonely trying to school all by themselves

hmm I do have snails. I've always kept trumpets, and random other ones, but I've never had dead fish disappear over night without a trace. They focus on the veg usually. I did get a new "racing zebra snail" yesterday, (my two year old loves to pick out snails.) so i'm not familiar with its eating habits. So I suppose it could have been snails... However, the cardinals looked great yesterday, the store is very reputable, and I watched them at the store for a while before I bought them, acclimated them slow. They were contentedly exploring and schooling well. I've no clue, but that's an awful lot of fish to lose in less than 12 hours (I looked at them at 2am when we went to bed, and checked them again around 11am). The remaining two look healthy, just lonely. Sigh.

Hmm.. good to know for next time. I knew it was common with neons to be fragile relocating, so i specifically got the cardinals. I'll see how the remaining two do, replace the hood for glass tops just to be safe, and try again in a few weeks. I was so excited to have some schooling fish.