You mentioned stringy feces. Did you treat for bloat? One of my Trophs had white stringy feces a couple of days after purchasing them so I soaked some of their food in a flagyl solution. Luckily they all ate it and I never had any losses. Touch wood!!!
Sorry for your loss, I hope the rest will be ok.
Yeah Zack, it sounds like you have "bloat" in your tank. Tropheus are tricky fish, as they are succeptible to this disease. They are very touchy about diet and water quality. Chances are the affected fish are not eating. Feed some medicated food to the ones that are, and treat the tank with Bakto-pur direct in tablet form from Sera. this is the most effective med I have found, don't wait, do it as soon as you can. Eliminate feedings for the next while as fish don't seem to get it if they don't eat. Sometimes the best thing to do is remove the affected fish before it spreads. Imo it is spread via the stringy white feces. I have seen this disease many, many times. Most of the times it is brought on by the wrong food. What are you feeding these guys?
The term "bloat" is a disease manifested by these symptoms
1st: the fish starts to hide, and lose interest in food, you may see it clamp one of it's pec fins agaist it's side from time to time.
2nd: The breathing will get heavier
3rd: the feces will turn stringy and white.
4th:The fishes stomach will take on a bloated appearence, even though it may not have eaten in days.
Imo it is symptomatic of a number of problems. It can be either bacterial or protozoan in nature. Or a combination of both. It is very difficult to treat in my experience.
the only fish I have ever seen with bloat are haplochromine (Tropheus, Mbunas, Peacocks,and the odd "hap")I've never seen any "lamps" julies, SA or CA cichlids with it either. Definately never in plecos.
NIce shot!