electric blue jack dempsy

Question
I recently started a jack dempsy tank. The first electric blue i bought died after about a week.  so i had 2 jack dempsy and 2 electric blue jack dempsy.  they seemed to slit and pair of one and one.  then about three weeks in the one pair turned up dead thought this might be do to teritory issues.  the other two were fine and then yesterday there was a white owdery loooking substance on the inside of their flower pot.  took pot out and cleaned it and tank.  the jack dempsy immediatly whent to the pot when it was replaced, thought at this time mabey it was eggs.  then a couple of hours later substance was back.  Left it alone this time and 6 hours later the electric blue was also dead last jack dempsy is doing fine, any ideas as to what is causing this.  the elctric blues are quite exspensive and i dont want to get more untill i figure out the problem if there is a solution.  thanks

Answer
Hello,
Jack Demseys should be kept in pairs or alone.  The name says it all, and they will kill any other fish if they have the chance in a tank.  Electric blues, although aggressive, and territorial are no match to a Jack Demsey.  He's still standing, and all your fish are dead.  He will kill more if you put some in with him.  Beautiful fish, but wicked, and very aggressive.  
Lynda