Fin rot or not?

[slick666]

I have a Striata that is part of a group. He recently received damage to his rear fin. I'm not sure is it's fin rot or something someone else in the tank may have caused him.

Here he is


Here are some close ups of the damage






My thought is since it seemed so sudden that it couldn't be fin rot. But sometimes you only see there heads sticking out so I supposed it could have been happening for longer than I think.

I also don't believe I have any fish that would fight in such a way.
Here is a list of all the fish in the tank
4 Botia Striata (1.5-2.5 inches)
2 Botia Kubotai (4.5-5 inches)
1 Botia Histronica (I believe, 2 inches)
1 Clown Plecostmus (2.5 - 3 inches)
1 Green Plecostmus (2 - 2.5 inches)
2 Pearl Gourami (3 inches)
2 Platies (1.5 inches)
These all share in a 38 Gallon tank (36in x 18in x 12in)

All the other Fish's tails seem fine (thank goodness) but I don't want this to happen to anyone else. I also don't know if this is damage that is permanent or will the fin recover at all.

Thanks for taking a look

[Diana]

I would increase the water changes as a start.
Whether this is damage form another fish or the beginings of fin rot the lowest possible nitrates will help the healing.
What are the most current water chemistry tests?

[slick666]

I will be testing the water tomorrow when I can take a sample to the store. I typically replace the water every other week so the water in the tank hadn't been replace in 13 days. I've already replaced the water because it was time so the test results will be effected.

[Diana]

2 weeks between water changes is too long, allows too much nitrate to build up between changes. This makes it easier for several different bacteria to get started attacking your fish.

At this time here is what I would do:
1) Do twice weekly water changes enough to get the nitrates really low and keep them down. Include some thorough gravel vacuuming to remove the remnants of fallen food and fish waste.
2) Get your own test kit so you are more aware of what the water chemistry is doing.
3) If the tests show any ammonia or nitrite let these be your guide to water changes: Keep the ammonia under .25 ppm and the nitrite under 1 ppm. Reading either of these indicates there is something amiss with the nitrifying bacteria.