Jeffysfish, I would suggest taking a water sample to your local fish store for tests. Most stores will do these free, some may charge or require a purchase of something... but that is one option, a second is to purchase a reliable test kit. The API combo is probably the best deal, it includes ammonia, nitrite, nitrate and pH I believe. The hardness test is usually individual, but there I would suggest using the store rather than buying a kit because once you know the hardness (both GH and KH) of your tap water it is unlikely to alter. Some water boards will tell you the water hardness; again you want to know both the KH and GH.
With respect to your original questing (first post), I think there are two possible--and both serious in my opinion--issues. One is the overcrowding, second is the hardness.
1077 has given solid advice on the former. I will only add that it is one thing to have 13 angelfish in a 50g knowing it is temporary and planning for the next phase, but quite another to expect those fish to be healthy long-term. Fish grow their whole lives, unlike humans. They develop internally (their organs) and their external housing grows to accommodate this. Keeping potentially large fish in small quarters is almost always detrimental; it stresses the fish which causes problems with the immune system and other physical development, and many believe there is internal damage done that may only be obvious down the road when the fish suddenly dies or develops other problems. Pasfur mentioned "stunting" and this is it.
There are two main reasons for this. One is the physical size of the space the fish is forced to live in, and the second is the quality of the water that results from overcrowding. Fish interact in various ways and from species to species. Pasfur made a good post in a related thread, it is post #33 in this thread: http://www.tropicalfishkeeping.com/f...d-dying-37083/
As he points out cogently, it is more than just the "cleanliness" of the water.
The other issue looming is the hardness. We (that is, you) need to know for certain how hard your water is. Angelfish are largely commercially raised now, and many hold that this makes them more adaptable to differing water parameters. I don't want to get into this argument at this juncture, but because I firmly believe it I must say that I do not share this view totally. I believe there is a limit to which most fish can "manage" with parameters that are vastly different from what nature built the fish to live in. I have elsewhere often written of calcium hardness causing blockages of the kidney tubes in cardinals and similar soft water fish; angels come from those same waters.
Depending upon the actual hardness, your angels may be suffering due to the hardness being greater than they can adapt. I'm not saying it is, but it is a possibility that should not be overlooked. At the very least, this adapting may put additional stress on the fish--as one writer put it, the fish has to work harder to maintain it physiological processes, and that means stress. The fish has a blood pH that it must regulate to match the water it lives in; an abnormal pH is bound to have consequences on the internal biological actions of the fish. Couple this stress with that from the closeness of the physical area and related factors, and you can see that it is compounding.
Please post the test results once you have them. In the interim, I believe you should consider the options to remove some of the fish from the aquarium in the near future. If they are healthy, the store may accept them in exchange. Or other hobbyists in the area. I don't think anyone can argue that this is not going to be necessary down the road if the fish are to enjoy healthy and full lives.