Life has a way of pimp slapping you in the face when you think everything is going perfect...Allow me to explain. So yesterday I wake up at around 7PM ( yeah I know, to say I'm a night owl would be an understatement) and of course, first thing I do when I go downstairs is check my tanks. And there it was, on my bronze cories, his grotesque white body floating lazily in the current. He was eyeless and finless, obviously, his fellow tank mates had used him as a snack after his death, my beloved cory, reduced to the fish equivalent of a bag of Doritos. So I immediately take him out of the tank with the net, and bury in one of my grandma's flowerpots, why do I do that? I don't know, it seems a little more dignified than flushing him down the toilet. I check the water, to see if something was wrong, and I have 0 ammonia and 10 nitrate. Pretty standard reading.
Then I think, maybe he just died of natural causes, maybe you didn't eff it up this time. And then I look at my other cories, I had 6 in total, of the surviving 5, two look completely fine, but the other three, I noticed their barbels were too short. One of them had a normal barbel on one side but no barbel on the other side. I think, how did this happen? The only answer I have come up with, involves me being a dumbass of course. Here's the thing, like a week or two ago, I decided my 20H needed something new, so in front of the driftwood, I put some white Kordon Wonder Rock. I also thought since this gravel was going to be smaller than the one I had, the wafers wouldn't get stuck in places the cories wouldn't be able to reach. Now I think that maybe this new rock is too rough for them, and that's why they been losing their barbels. It's just an idea, you guys know way more than me and perhaps can tell me what happened.
Here's a pic of the Kordon Wonder Rock:

And here's a pic of the area where I put the rock.

Could that have caused them to lose their barbels? Now that I have 5 cories left, will they be OK like that or should I add one or 2 more? Are the cories with short or no barbels doomed? Thank you for answers.