I had a pair of Potter's in my 58 for 4 months, and were doing great. I lost them back in March when my main pump failed, or ran dry. I had to go into the hospital for an unplanned surgery on a Saturday evening. Had no time to get a reefer to watch the tank. So I just had my father stop by my place to top off and feed. I believe 2 days before I was released the pump stopped. When I came home the were both dead. The temp was 70* (( normally 78*-83*)), and the SG was at 1.030 (( normally at 1.026 )). The other fish -- pink skunk pair and golden algae bleeny were fine. My 2 Haddonis even were fine -- though one of them spawned the next evening. It seems to me that they are very sensitive to any parameter being out of the normal range.
Prior to that pair I did have a single one (( in the same tank )) that was doing great for a couple of months, and was dead one morning.
I currently have a small one in there that is doing wonderful. I am attempting to pair it, but the larger one still hasn't eaten any prepared foods after 3 weeks. But, so far it is otherwise acting normal, and picking at the rocks.
IMO, one of the important things is to have a "old" tank with mature live rock, with a decent amount of algae on the rock for the fish to pick at.
As for QTing, them.... First, I should note that I normally don't QT my fish (( wild caught clowns are QTed )). I did it for 4 days with my current small one, and it was only doing okay, eating but not with gusto. Right after I put it in the main tank, it started eating like a pig. So, if someone does choose to QT a Potter;s, I think it is best that the QT be as close to a normal tank as possible --- lots of hiding spots, and some aged live rock to pick at.
I have noticed that they seem to have smaller mouths then similarly sized dwarf angels, so that will have to be taken into account. I feed mine 3 types of Rod's Food (( red, green and blue labels )) Prime Reef, LifeLine's herbivore mix, and Spectrum pellets.
Believe that keeping them in a full reef tank is the best choice, mainly due to better (( on average )) water quality, and algae to pick at. In addition I feel that they do better with less aggressive fish. Oh, and I wouldn't want to put one is a tank smaller then a 58, mainly due to the fact that a bigger tank will (( at least most of the time )) have more live rock, which provides more natural food.
Lastly, it has been my experience that the small to medium sized ones adapt better then the larger ones, though that seems to hold true for a lot of fish.
Some pictures over the years,
My current wee one, during its few days in QT,
The PVC is 1 inch,
The pair I lost to the pump
Female
Male
Together-ish