>=( Hercules has finrot?????

[LittleBettas]

So, Hercules fins have been growing back SOOO nicely, so I decided to upgrade him to a 3 gallon tank 3 days ago... (he was in a 1 gal. QT qith 100% water changes and AQ salt due to his torn fins)
Well, this morning I noticed he had fin rot... I put him back in the 1 gal QT tank...
but I was wondering what would have caused the fin rot???
its located only on his bottom... I'll post pics in a bit

[betta lover1507]

if it is grey-ish tips or red tips it has to be fin rot or body & fin rot i seened that before='[ (to many bad memories)

[LittleBettas]

They are blackish, I have another fish with fin rot, it just sucks because he JUST got out of QT and having 100% water changes, I was doing 100% water changes every other day in the 3 gal. he was in.... no clue how he got it unless it was stress from the new tank