I am very glad to see all the success stories. I have to agree, I have a 3 1/2" hippo now that has been absolutely, knock on wood, ick free, going on 6 months in the display tank. I have however, been the parent of not so healthy hippo's....mostly smaller versions. Their quarantines were all the same, with different outcomes. I am convinced that some of the hippo's collected are just like us humans and do not adapt well to change. Thus stressing them out, and ick appears. Tangs are not the "dreaded ick magnet" that everyone seems to feel they are. They just need the proper environment and tankmates to make them feel at home and relaxed. Of course, starting out with a healthy fish is key. Just my 2 cents.
But swaziland, honestly, you are asking for trouble with a hippo in a 40g.