Dwarf Gouramis/disease

Question
Hello William.  I've had 2 Powdered Blue DG's for 1 1/2 months.  The male died last week and the female (knock wood) is still very fine.  I added another 2 females about a wk. ago and one died the next night.

So...there's 2 females in the 29 gallon along with 6 Platies and 4 Panda Cories.  The NEW female that is alive is ok except for odd head jerk once in awhile.  Strange, because my male had that as well before dying.  The original female is looking very normal still after 1-2 months.

Are these 2 females going to end up dying as well?  I've heard it's 50-50 and some say if one dies of DG disease, they're all doomed.  I was told the fish don't come from Asia but from Florida farms.  Probably just as bad there too.  

By the way, I have no ammonia, no nitrites in tank and it's syphoned 20% once/week.  I add conditioner to water too.  I feed once daily usually, sometimes twice, a varied diet.  

The only thing I don't add is aquarium salt.  I've been told it's not needed as these fish don't swim in salty water and it's bad for Cory catfish.

I sure hope you can enlighten me or give me hope my DG's will live healthy lives still.

P.S.  I like these fish so much, I've gone and added a male/female (so far) to another tank, a 20 gallon LONG with 5 platies.  Now I've got my fingers crossed for them too.  I wish I had've known about this -------- disease beforehand!  They're ok still but it's only been 5 days or so.

Any help would be appreciated!!

Answer
Hi Paula, I am not William, but this question was in my box this morning.  It's January 9, and I do not know how long it's been in the pool, but it's been referred to me by other experts at this point.

I hope you don't mind my answering. :)

I would add a teaspoon of salt per gallon.  The fish don't have this in the wild, but next time you change the water, as you change it out on your weekly rounds, it will filter it out eventually entirely.  It will help prevent parasitic attacks, which it sounds like might be an issue.

If the head-shaking continues, then he has an "itch" and I would assume there is a parasite lurking somewhere, or a light bacteria.

If you don't want to use salt, please consider using Quick Cure.

Good luck,
Renee