Woke up this morning and my White Convict had died

, I'm gutted and feel like I failed to take care of him. The white lumps were still present wish I knew what they were.
Thanks for your help Barb, I followed all of your advice and he seemed well in himself untill this morn.
I've done a full water change in my main tank and changed all of my filter medium, I disturbed my substrate as I was emptying my tank and syphoned it, but didint clean it totally as wanted to keep some bacteria. I have used a chemical in my filter to help with the bio and I will test my water daily, any other advise? I felt like disinfecting it in case there was a parasite in there waiting to get on another fish but bleach isn't good for fish lol so I didn't, but I did clean it as much as poss. I have added some melafix as I usually do when disturbing my tank in any way.
I am still treating my Acara as he got into a fight with my convict and the convict pulled part of his lip off, I am using Myxazin for this, he just has three days of treatment left.
All in all I have lost four of my fire mouths (all of them) and my White Convict, I had raised them all from tiny babies and feel like I have lost my kids, its awfull. This is the down side to keeping fish hey, looseing them when ur not entirelly sure why!!!!
Good news is that I have just bought another tank, the Jewel 400 its about 400 litres, not sure what to put in it yet tho!