Okay the post keeps disappearing lol,
Here we go again with the 3rd time of me trying to post, the OP has stated that it's every 3 days or so after they notice gill damage, as I said I'm not saying it isn't but type 1 will wipe out a stock in 24 hours when I had it I treated my tank with the meds people on here said to use and my fish still died Over a 5 month period.
So to the OP, if it is indeed columnaris you need to do a few things, if your tank is on the warmer side you need to gradually lower it to 75 as columnaris spreads at a slower rate at a lower tank temp, but spreads super fast at a Warmer tank temp
Second is treating with kanaplex and metroplex Reason I say metroplex is furan 2 kills BB Really fast and can be overdosed where as metroplex is a much safer med, also remember treating with these meds can cause kidney damage so if you go this route dose every 3 days not every one.
yoyo loaches killing them which is very plausible as I have witnessed loaches killing other fish just cause they want to, I'll give you an example of an incident I had.... I bought 2 BN to go with my Calico BN I already had in the tank, woke up the next day they were dead my LFS refunded me for them I bought another one acclimated it put it in the tank with the lights off and I immediately saw my Calico go attack it, did some research and found pleco's will attack other fish that look like them, when I posted about it I was told it was "columnaris" it wasn't it was my BN killing them, watch the tank with either lunar blues (if you have them) or low light make sure you're out if sight and see if the yoyo's are attacking them.
Third is one you will not like to hear but it isn't mandatory, when you see an ill fish the best thing to do (from what people told me on here a year ago) is to euthanize it immediately, when I had columnaris the bacteria itself didn't kill half of my stock I euthanized most of them when I shouldn't have, I did however euthanize the ones that were pinecone scaled because there's no coming back from that so that was indeed a must.
You can do kanaplex +furan 2 just be make sure it's loach safe, and if you have inverts they have to be removed.
Treating Bacterial Diseases with Seachem Kanaplex & Metroplex — David's Aquarium Advice