Tomorrow may be too late honestly. Velvet works fast.
You may be a candidate for this experimental parasite management technique that was developed on the humblefish forums. Uses peroxide, carbon (maybe not necessary but recommended) and ideally a dosing pump, but for an emergency manually dosing should do the trick until you get a dosing pump if you don't have one. It's reef safe and invert safe. It works by oxidizing the parasites when in their free swimming state and suppresses further infections until eventually the population of parasites fizzles out. Read up and make sure you do it right. Lots of trials and reports in that thread. It may have negative effects on some aspects of the tank's microbiome but I don't think enough to let all your fish die.
***Current dosing recommendation for active outbreaks, using 3% hydrogen peroxide*** (a TLDR for people who just need to know how to get started) Week 1: 1mL/8g, 3x per day Week 2: 1mL/5g, 3x per day Week 3: 1mL/5g, 3x per day, plus overnight dosing. Continue the week 3 dosing regimen for a...
humble.fish
This may be the best way for you to handle this. And the people who have done it seem to think it has a better success rate than trying to fish everything out into a copper tank.