Strarving Electric Yellow Mbuna

Question
Hi, I have a 30 gallon fish tank .Yellow Lab,Acei,Bumblebee,Red Zebra,Kennyi and Chipokea They are about the same size (well almost the same.).They get along very good.But I noticed that the Yellow Lab is not getting bigger last 2 weeks .And it getting thinner .I thought some bulling is going on but not like so ..All the other  are swimming around but Yellow Lab is not .When the meal time it is like the last one to come up . Then he has a problem eating  seems can't chew or swallow .  So I desided to feed them very often very snal amount so he has chance to eat a little .(Tiny bit of flak food )
Today I noticed it is always on top looking for food .So I tried to feed it but its gaw is oddly shaped and he is really skelleton like now .
This tank is 2 month old and I was having hard time cycling quality of water to 0ppm on all 3 categories because I was moving fish around to or adding to make a peacefull bunch .Yellow Lab and Acei was my first fish and Yellow Lab has been very aggressive to other fish .Now Acei is twicew bigger than Yellow Lab ..Do you think there is some disese going on? All are no ripped fins healthy eating habbit .Actualy they look all good except Yellow Lab.They are not fighting during the meals or picking on each other any time .
Should I separate YEllow LAb.?

Answer
Hi Lucy
If you have a separate tank, go ahead and move the sick one.  
Does he look like he's breathing rapidly/gills moving fast?  

It's probably too late for him if he's that thin, but go ahead and add some salt to his new tank, dose at 1 tablespoon per 5 US gallons, and see if that helps any.  

Christy