stinks, big time!

[plecoL83]

Yesterday I found my albino bushynosed pleco dead on the bottom. this is my second loss of a pleco in a month. First my L83 then my b/n. my water is fine 0 N03, 0 N02, 0 ammonia, Ph 6.8, Gh 75 ppm, Kh 75 ppm, I was feeding them a pleco food tablet every 2 days along with cucumber or zuccini whenever I had some, along with algea to eat they appeared perfectly healthy. not ematiated and always coming to feed. Any ideas anyone. I'd love to hear for the sake of my bulldogs. (plecos)
Pleco L83,

[beowulf]

Any sign of damage?  Could one of the surviving plecos be a bully?