So I posted before about my betta having a small pin hole in his back tail fin. I was told to just keep the water clean and watch for fin rot. A couple weeks later the hole was 2cm but there was no rot anywhere and he was otherwise healthy. A week later from the edge of his tail fin tore in about a half inch right in line with the hole. The hole has now torn wider to about 4cm and if it rips any more, it will join with the rip from the edge of his tail splitting his fin in two.
His fins are otherwise healthy, no rot, no chunks falling off, just this one weak point mid back fin that's not been healing! He eats fine, swims a lot, and there's nothing sharp in his tank for his fins to catch on. The water is changed once a week, and is typically crystal clear (except for a couple weeks ago when it went milky with a bacterial bloom after a cleaning that settled on it's own after 5 days). (He lives in a 5g heated + filtered tank with a baffled filter so the water is calm)
EDIT: Hes a vail tail fyi
Should I be concerned with this fin splitting into two? Is this natural, or a natural weak spot that will just eventually split his fin? It's been weeks and no signs of infection or sickness, just the rip getting bigger randomly. Should I be treating with something? if it does eventually rip from fringe to the base of his tail, will it ever heal back together? Since it's been so long with no signs of healing, I'm just worried.