I appreciate the response. So far so good. Everyone is healthy and happy so I think I have to go with the lighting being the problem. All I have is a 14W Bulb over the tank. However, it is placed in the kitchen which gets lots of light from the sun naturally during the day (Did this on purpose since 14W just doesn't cut it in a 28G Hex.) Green algae seems to flourish and my remaining Oto seems to love it! Maybe the other guy was just sick and that's all there was to it. Oh well, I'll be purchasing a few more otto's come this weekend for my algae clean up crew.
(Mental note: Remove UG Filter and add live plants. Natural Lighting should be good in the kitchen, Right!?)