Made the same mistake! Just my experience not to discourage you, but it took a good month to 2month before chaeto grew again after stop dosing vibrant. The one that was in my Refugium completely melted a month later I added a new ball, with no success either. Only now I see robust macro algae growth. Also if you chaeto is melting it will release all of the nutrients back into the water column. Why did it take that long? Vibrant is mostly a bacterial product, these bacteria will settle and grow on substrate and as such doing water changes will not get rid of them. So they have to run it’s course. My suggestion would be to pull your chaeto and wait a few weeks or a month before reintroducing any macro algae, but it just my two cents.