Discus having Some Symptoms

[Luna]

Hello my friends, this is my first post here. I have been looking for some kind of form to fill out about my water params and my fishies symptoms, but I haven’t been able to find one so if there is one that will be helpful o would be grateful for a link or some direction. I have 6 discus (and a handful of blue rams, 2 gourami, and kuhli loaches) in a 75 gallon tank. About 24 hours ago I did a large water change (I do 50% 3-4 times a week), and my discuits have been flashing and darting ever since. I introduced them to the tank in two groups of three and the first group had absolutely no problems about 3 weeks ago. At this point I’ve had the second group of three in the tank for about a week and now I’m noticing some things about my fish. Here’s where it gets a little tricky because I’m not sure where some of the symptoms started. I’m not sure if I didn’t notice because I was generally unfamiliar with discus at first or if they appeared recently. I’ll make a list
Symptoms:
1. Flashing and darting after 50% water change using seachem prime. The nitrates were a bit high before this water change, between 10-20 ppm on the master test kit. I think this is because of a build up of decaying plant matter and a bit of over feeding the day before. I vacuumed the gravel very throughly. Before that water change I had never seen that behavior which was the reason for my alarm. The same day as that water change I added a new submersible canister filter for water polishing.
2. Shivering! Tails and dorsal fins for the most part. The shivering, darting and otherwise frantic movements outside of general aggression I know are new for sure.
3. Clamped fins, but only one at a time. I had one fish that was clamped shut when I first put it in but has since adjusted, but this has shown up in all of the fish at some point, even if it’s not too consistent.
4. Slight fin damage: two or three of them has some slight fraying on the tail and dorsal fins I originally credited that to some aggression, which I lightly scolded all 6 fish for, but now my favorite blue boy has a hole in his fin. From my understanding that’s early fin rot but I honestly can’t imagine the params being poor enough. I test the water once a day and change it often (I work from home and when I’m bored and thinking of my fish it’s water change time).
I do fill the tank directly from my faucet with my hose, but I’m very careful to match the temperature and dose with enough conditioner for the whole tank gradually as it fills.
5. I’m pretty sure my favorite blue boy also has some holes in his face, which makes me really sad. This is the main one that I don’t recall if he had it when I got him. I picked them all up from the same LFS, but they don’t specialize in discus or anything. I loved the fish so much when I picked them out it never occurred to me to check the store itself for good husbandry.
6. Lastly there are some things I’m not sure are legit or if I’m worrying so much I’m seeing things now. The fish are being more aggressive toward one another, they were a peaceful little school of cuties for a whole week and now they’re being so rude to one another! I’m also concerned about some cloudiness on the edges of some of their fins, and a single fish popped something sorta clear and white-ish but the rest of them seemed fine.

I did jump the gun a little bit on treatment I think. I threw out the frozen bloodworms I had been feeding them. They eat frozen brine shrimp and some cichlid pellets still at the moment. I dosed the brine shrimp with API General Care since I convinced myself they had some kind of parasite, and I also followed the treatment instructions for the entire 75 gallon tank. I do wish I waited until I made a post like this to start that in hindsight, but hopefully it hasn’t stressed them out too badly. I have also increased water changes, removed carbon, keep my bubbler on 24/7 (instead of just at night). I am certainly worried about them, and think I have reached the end of the advice I could get from frantically reading articles on the internet. Any advice you have or resources you can share will be greatly appreciated!