Many ich treatments are ineffective, but not all. Let's see what the name of the treatment he's using is.
thumpco, I went and read some of your other posts. Looks like you're learning some of the pitfalls of this hobby the hard way, but don't give up! It can be extremely rewarding if you research your choices before hand. First, I'm sorry to hear about the ich outbreak. I'm sure it started with your tang, since he was most likely stressed and susceptible to the disease. I know you said it spread and killed your clowns...did it eventually get your firefish goby as well, or is that one still kicking?
I have some bad news. 5 weeks of ich treatment may not have killed the parasite. Marine ich has a specific life cycle, including a medication resistant cyst stage that can hang out in the sand bed for weeks before "hatching" and getting in the water column again. If the tank is fallow (empty of all fish life), the common rule of thumb is 60 days if I remember correctly...perhaps 90....of no fish before it's safe to introduce new livestock. This will ensure that any cysts will hatch but die off because there's nothing to attach to.
If you introduce new fish now, you may be risking a new disease outbreak. If you choose to do this, I recommend you go VERY slow. Especially if you can't QT the fish first. If *I* was stocking a 37g tank, I would probably consider either a lemonpeel or flame angel (one or the other, NOT both) as my "showpiece" fish, then I would consider a royal gramma, a pair of orange-lined cardinalfish, and possibly a pair of greenbanded gobys. If you still have your firefish, I would nix the RG. In order to stock the tank slowly, I would introduce the Gramma first (again, assuming the firefish is gone), and wait a full month. If the firefish is still there, then start with the two cardinals. Again...wait a FULL month and observe the fish. If no disease is present, add the two greenbanded gobies. Wait a month again. I know this seems like a lot, but we're doing 2 things by waiting. 1st, we're assessing how disease-free your tank really is, and 2nd, we're letting your biofilter build up between each addition. Finally, you will add the most aggressive "show" fish...the flame or lemonpeel.
Again, that's just a sample stock list. Your mileage may vary.