Most of the dips , like the ones
@vetteguy53081 reccomended are actually designed to be used with qt in a way. Mild and frequently needing redipping. This may now me considered not effective in age of dip and hope. Ie Bayer And into the dt(and hope the eggs don’t hatch)
A qt if the first line of defense. The qt, keep in mind , is meant to be nuked. For example , zoa nudis. If the eggs hatch , you can dip to kill em and scrape eggs agin and agin , or in qt you just use flat worm exit. Nukes it like Bayer. You can do that to a DT. But there’s a lot of life you want that will be killed. Pods worms etc.
same goes for algae. There are some very harsh algecides folks won’t use in a DT any more , instead look for fluconazole and vibrant as it’s mild on the DT.
So , if you get a frag , dip in a good but mild dip, and clean up the frag but bubble alge forms redip and scrub, but it spreads in the qt, you nuke the qt tank and save the DT.
This also allows for the choice of benifical or just plain cool hitchhikers. Like worms and stomatella snails acro crabs etc, to be found and added to the DT.
So it’s not a 100% guaranteed thing but allows for a buffer between dirty or unknown systems.
New live rock actually can be cleaned and qt in the same way in a bucket.
As far as fish parasites , it’s the same 72 day fallow , in coral qt or bucket. Myself , If it’s a must have cool rock, it’s probaly faster to kill it and recycle it in a bucket than qt.
And yea , sadly , it takes the fun out of impulse buying.