It is as I suspected. There is definitely a protozoan problem here, accompanied by a secondary bacterial infection. Thank you for the new photos, that really helped a lot in diagnosis.
My suggestion is going to be to treat the entire tank with both metronidazole (and if you can coat the food with it at same time even better) and also triple sulfa. I am not a big fan of triple sulfa, but for these species of fish this is the most effective medication that will be safe for all of them. This combination does have the potential to cause harm to some of your live plants, so if you notice the plants having a problem I would remove them. Plants can be floated in a bucket of water with a light over it (I use rubbermaid tubs for this type of thing) to get them through until the end of treatment.
Please be careful not to overdose either med. If you need instructions for coating the food please let me know and I can talk you through that. When working with the triple sulfa it is extremely important that you avoid skin contact and inhalation. A great many people are allergic to this stuff and the reactions can be severe enough to send you to an emergency room, and it can be very painful. Latex gloves, something over your mouth and nose, and protect the eyes when using it. This medication is a powder, so dose it in a well ventilated area but in a place where there is little air current (so it doesn't blow around).
When dosing powdered medications its important to do so in a cup, add a small amount of tank water and swirl gently until all medication is dissolved in the cup water. Be patient as this may take time, not all meds dissolve as quickly as others. Be sure to use a cup that can be thrown away when this is over, but avoid anything with a wax coating, such as Dixie cups. Plastic is the safest. Once completely dissolved in the cup water, empty this into the tank in front of the filter's waterflow into the tank so it ensures good circulation, or in front of a powerhead. Avoid pouring it in near an filter intake, such as with a canister filter.
Dose and mix in the cup each medication separately, so as not to mix both chemicals in the cup water at once. The high concentrated mix and dry mixing of these meds in the cup can be dangerous and cause unwanted chemical reactions. So, dose one, get it into the tank, rinse the cup good in the tank's water and then begin again to dose the other medication, and yes, both meds can be used together in this way.
Remove all carbon from your filter(s) during treatment and follow instructions on the medication containers. So the first day you will dose both meds, then dose according to directions for each during the rest of the course of treatment, following the time line and water change schedules each med offers. Treatment should continue for at least 3 - 4 days after all fish appear to be healthy again, this includes fully healed fins. If you stop the meds too soon you may find you have to do a 2nd course of treatment... and in the mean time you may lose more fish because of how fast this infection is moving. Better to go an extra day or 2 of meds than to have to go back and start over from the beginning again.
If you cannot find one or both of these meds please do not substitute another instead. Come back here or pm me and I will either help you find them online or I will attempt to find another safe med to replace what you can't get. Not all medications can be mixed, so please... don't take any chances. Some meds, when mixed, become toxic to the animals, and some of them, when mixed, become toxic to you or can cause chemical burns, explosions, etc due to chemical reactions. I practice safety first... always!
Best of luck to you. If you need further help please let me know. I am down with the flu right now, but will make a point to stop in and check on this thread at least once/day for the next few days. You are always free to send me a pm to get my attention flagged in email, which will bring me right here to your thread.