Red mark on ranchu

[Huihui]

Hello, I'm new to this thread and have some questions about my goldfish. I have a ranchu and yesterday I notice a red mark/ scratch on his belly, and I'm a bit concerned. Yesterday I check it was a tiny mark and today it looks redder and bigger, I'm not sure if it's blood or anything. But he acts very normally like eating, swimming around and stuff. Should I use methylene blue or an antibiotic to help him? I'm also not sure if he just scratch himself because I have a bare bottom tank, I do have a filter with like the sucking part out and is not covered by a sponge or anything, so I'm not sure if it was the plastic part of the filter.

[Colu]

Looks like an injury I would add aquarium salt 1 table spoon for 3 gallons and monitor for 1 week just remember to only put the amount of salt back in that you take out so if you do a 2 gallon water change put one table spoon back in if it starts to get worse after then over the course of a week I would then treat with antibiotic medication like kanaplex in food

Edited April 5, 2022 by Colu

[Huihui]

Here is a close up of it

[Colu]

Looks like an injury to me I would go with the salt for noe and follow up with the kanaplex in food if it get worse