No, in a filterless QT, NH3 can build up in less than a day. Weekly water changes often aren't enough. As for HOB filters, they can also be HOF or HOS, you don't need to put it on the back. At this point there's no point, unless you have a piece of mature filter media. It's a good practice to keep a foam block in your sump for times that you need it.

But what does a filter do that my live rock doesn't?

Circulates water more efficiently through the media. Given the lack of filter, a fair amount of smaller pieces of rock (~10 pounds) would suffice. So if you have a single piece, I'd probably break it up to increase surface area.

I typed that a little too quickly
Didn't mean it to be snarky

Hang-on filters remove lots of detritus, and can also be used for all kinds of media
They're easier to deal with than LR

Water just tested 0 for nh3 and no2 on elos kits, didn't bother testing for nitrate. I think the live rock route is working for me, I have about 6 lbs, the ugly stuff from my sump that isn't display worthy. 550gph of circulation and the tanks being aerated. I see no difference between this and having a mechanical filter.

Essentially, there is no difference, although a mature media filter can work faster than rock. And filter media can be re-usable once you're done with it. Rock, not as easily. If you've used medications, it may be too deeply adsorbed into the rock pores to remove. Foam blocks can be bleached and re-seeded. But, if it's a one off, you have spare rock, and it does the job, that's all that matters.

I guess for medicating purposes it's definitely more beneficial to have a filter. I could buy 50 filter pads for what the rock cost me. But this was kinda a make do rushed tank to try and rescue a tang. Once he's better i'll have to reassess the setup and most likely relocate to an area where adding a 10 gallon sump would work. Then I can filter and protein skim. My tank is getting to the stage now where it's not worth not quarantining. Thanks everyone for the input. I'll update in a few weeks an let you all know how the tang does. Hopefully it all works out.