White spot on fins

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I have 6 silver hatchet fish. Started with 4 ( been fine for weeks now). Recently added 2 more a few days ago. When I got them home they were noticeably bigger than the 4 I currently had. the one had one white spot on each side fins...... Not specs all over and it wasn't fuzzy. The spots were in the middle of the fin. The next day the spots were the same size but had moved down more toward the back of the fins toward the tips. Today its as if it's dripping like off the tip of the fin. It's part on the tip and part in a drip like shape hanging off the fins. One side has more than the other. My original 4 are still fine. The other of the 2 I just got looked like it smashed into the glass lid this morning and was hanging alone all day and died a bit ago and I took it out after it died. I don't think it was related but thought worth mentioning. They all have been eating fine. I am unsure if to remove the one that has the stuff on the side fins or leave and see if it goes away. My biggest concern is my 4 original fish because they have been doing great. Any help would be great. Going to see if I can get a pic that has enough detail to be useful.

20h planted tank, was 6 now 5 silver hatchetfish, 6 red cherry shrimp, 1 clown pleco.
Ammonia=0
Nitrite=0
Nitrate=0

 

[Filter]

I did not notice it until after I had put them in the tank or I would not have added them.... Was reading through my post and realized I didn't mention that.

 

[dkpate]

When I got some harlequin rasboras, they all looked like they had white stuff on their pectoral fins, and they were clamped like someone had taken a lighter to them and melted them. I used Melafix and Pimafix for about 8-9 days, and it cleared up. They were fine after that. The first batch I got, 5 died before I figured out what was going on, used the same combo and the ones healed up and survived.