What’s wrong with my ram?

[Ash1176]

I'm wondering what might be wrong with my German blue ram.
Tank is about a month and half old, fishless cycle, fish added this weekend.
Ph 6.8, amonia 0, nitrite 0, nitrate 20ppm
Temp: 80
Just noticed this tonight, his dorsal fin is really folded or even gone, and there's a big white patch on both sides. Fish looked perfectly fine this morning. Is it fin rot ?
Lost 2 cardinal tetras over the last few days, also got them this weekend.
Any help would be appreciated

[kevino]

He should be at least at 85 degrees F. it looks like he has a bacterial infection that will likely kill him if not treated with em erythromycin. did you quarantine him?
you should set up a 10 g quarantine tank . unfortunately you cant buy erythromycin any longer but you can use salt.
good luck

[Mike L]

Are you certain your nitrate is 20ppm. If using the api test kit which you should be, make sure to shake the heck out of both bottles for about a minute. Bang  the base of the bottles on a table. The agents in that test are prone to settling rendering the tests inaccurate. How much water are you changing out and how often too?

[Ash1176]

Thanks for the reply's, sorry it's been a bit of crazy busy week, on top of the pandemic... sadly he pasted away, looks like it was a case of columnaris which would have explained the 2 other cardinals dying...
Temp was 80 as there were other tank mates that couldn't really go higher.... I have now dropped the temp as other tank mates can go lower now the ram is dead, and also helps against columnaris... all other are fish are doing fine so far, it happened so fast. Appreciate all the help