Discus died!

So one of my newly acquired discus just died today and another one does not look happy at all, Im afraid it might die too.
So details first my tank is 54g with 20g sump, so 74g of water total.
just checked my water parameters they are good
Ammonia 0
nitrite 0
nitrate 0-5ppm
ph 7.2
So I bought a yellow thai discus 3" about a month ago and was the only discus till about 4 days ago, he was super healthy and had no problems
being by himself, ate from my hand and was always front and center of tank. 4 days ago I got 2 more 2" discus from a lady in renton, she had them at 90F
and her tank was way overstocked too(30g with 6 discus, 4 angels, gold pleco, random tetras and knife fish, ), I dont know why I bought them off her but they seemed healthy at the time. acclimated the fish really carefully, they were a blue diamond and a red pidgeon blood, by the 2nd day the blue diamond looked sad and his colors darkened. they were both being bullied by the yellow thai. now out of nowhere the red one dies and the blue diamond is the dominant one, my yellow thai is now darkened and does not want to eat
any help would be appreciated thanks in advance

What temp are they at?

84F

90 is way too high for any discus!!! I would have walked away.....

I use to raise dicus and went through all these same issues, with my experience there no different than any other cichlid. They have a pecking order and also are a schooling fish, the problems your having is by introducing not a big enough group of them to spread out aggresion. I tried 3 discus and it never worked until I had 5 or more so they formed a hiearchy. I would recommend finding some place cheap where you can pick up 3 more and take the yellow thai and put it in another tank till you can get more. When you get a total of 5 or more then do a water change and rearrange your tank and acclimate the new discus plus the yellow thai again. By do the water change and rearranging it will disturb the dominancy of the tank and allow time for all the discus to re-adjust to each other before they form a hiearchy.


What other fish do you have in the tank with the discus?

You should always quarantine your fish for at least 2 weeks before introducing to you other fish. I used to breed discus as well and they are notorious for internal parasites or gill flukes. In your case, I have to agree with Addictedtofish, with only 3 discus, now 2, you will soon have only the dominant left. Move the blue diamond to other tank right away and the yellow thai should recovered. Raising the temp of the tank will also help the recovery process. Even with a group of 5 discus, you will notice soon that 1 will hardly grow and becomes a runt. If you remove the runt, the next smaller one will become that 'runt'. This effect goes away if you overstock the tank, it is a matter of aggression. The lowest one in the hierachy just doesnt get to feed as often.

I keep a small school of
cardinals(7)
blue ram
apisto agassizi(2)
apisto iniridae
apisto cacatoides(2)

so the disease whatever it was is now gone. I treated with salt and melafix for 7 days
the yellow thai recovered, but i lost one agassizi and one cacatoides as well.
I leaned the hard way that you should quarantine new fish.
I know I should have walked away, now I know better.
So do you guys think that I could keep 5 discus along with my tetras, 3 apistos and ram
in the tank?

wow small world im the lady that sold him the discus. I feel bad that one died. And no my temp was at a normal 84 just the stupid digital thermometer was broken. I got those fish like 3 days before he came and got them from me from some guy in everett. he had a whole bunch of discus about 10 in a smaller tank than mine. Thats why i decided to sell a few of them because your right it was over crouded and i realized this when i put them in the tank. The other discus that i kept that was in the same tank are all still doing really well and i have had none of mine die.

One big factor I noticed was your pH. Discus thrive in LOW pH. Somewhere between 5 and 6.3 pH is preferable. Adding more logs to lower it is one option. Are you using any Black Water or anything for buffering? I think that the temperature is fine, nothing above 86F. Are you giving them a variety of foods as well? Discus can actually stop eating and die from consistency. What are you feeding them? Good luck