Vinegar problem

what kind of buffer are you using?
what are you using to test it?
whats your ph out of the tap?
how long has it been setup?

hey phil, higher pH has nothing to do with your use of vinegar. vinegar is essentially acetic acid and if anything, would lower your ph rather than raise it. what was your pH 'before' this incident? what is it now? what's the pH of the water right out of your tap? use of "balancer" and other 'chemicals' is not a good idea. it leads to instability of your water chemistry.

rinse the tank again with warm water.

Since the tank had a 100% mortality rate, I would reccommend you bleach sanitize everything. Just fill the tank up and add 2 cups of bleach per 10 gallons and just let the tank and filter run for 2 hours. Then drain and rinse everything well. Let the tank air dry and then refill. Double dose on the dechlorinator to get any residual chlorine that did not evaporate during the air dry stage out. After that fishless cycle the tank to prepare it for fish and add your full fish load at once after the fishless cycle is complete. Don't add any live plants yet. I then want you to treat the tank with salt (pretend it has ich) for 14 days in order to de-parasite the fish (Salt kills 14 different unicellular parasites including ich) and the salt will also help the fish adjust to their new homes. After that you can waterchange the salt out 40% waterchanges at a time if you want. Every fish I add to my main tanks undergoes a minimum of 14 days of salt treatment in the QT tank and I never see ich in any of my tanks as a result of a successful QT process.

Edit: Don't treat them with any medications pre-emptively. Salt is fine and I highly reccomend people to QT their fish and use salt as part of the process. Medications are not fine unless you see a need to use them like an active infection.