BEGINER'S GUIDE

Discus are generally very pretty, but they also cost more than most other fish. First time / prospective discus buyers are usually overwhelmed with the many different color / pattern strains and often go on emotional response as to which fish to get. They also usually go to their local fish shop (LFS) to purchase their first discus. Unfortunately, many times the store employees are not experienced in keeping discus and will unintentionally give the wrong information. To make matters worse, the discus at many LFS will not have been kept in optimal conditions either.
Here are some photos to help you choose/ select a good fish - regardless if you choose your fish from the breeder's fish farm/ hatchery or a good LFS. As mentioned before, do your homework first. I've seen several newbies/ beginners decide to jump in and get discus only to find out they have ended up with a lot of problems (sick or dying fish usually).
I've also seen many beginners proudly show their newly acquired fish off on forums, only to be told by more experienced discus owners that the fish isn't the "beauty queen" that they thought it was. Embarassed, the beginner will say, "I'm not looking for a show fish" and sympathetic people will say, "if you're happy with it, that's all that matters"... which may be true, however, if you've spent good money on a fish that is supposed to look pretty, shouldn't you get your money's worth? Also, shouldn't you get a fish with the potential to grow out to is fullest maturity and look nice?
Finally, no matter how pretty the fish is or how much you want it, do NOT buy it if it's sick and don't buy any of the other discus sharing that same tank. Period!

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Discus Heads. Look at a discus fish straight on/ head on.  If their foreheads are pinched. Do not buy that fish  (or any other discus in that tank). Chances are that the fish  hasn't been eating well and may have internal parasites or other problems. Also many people prefer fish with a nice smooth  round profile without any indentations near the eyes. Lastly,  pay close attention to the gills and gill covers - if they are  breathing very hard for no apparent reason, gasping at the  surface, or breathing from one side only, they possibly  could have a heavy infestation of flukes or even a bacterial  infection.

Discus waste. Healthy discus feces (poop) should be dark  if they've been fed beefheart, sometimes red if they've been  fed pellets, and you'll see undigested bloodworm skins if  that's what they've been eating. If a discus has long white,  stringy feces, do yourself a favor and don't buy that fish.  Chances are it has some intestinal problem, infection,  or a parasite like hexamita or even tapeworms.

Body coloration, skin, and fins. Discus should appear on the  brighter side, if they are dark or if you see gray patches of  slime peeling off, they could have either a bacterial problem  or a parasitic problem (such as flukes, costia, or chilodonella).  Also, their fins should open up. If the dorsal and anal fins are  clamped, have a ragged edge, and their tail sags/ droops,  chances  are that's a sick fish. Believe it or not, the two fish below are  of the similar strain as the one below it (the first column are  red turquoise  type fish and the second column are solid blue type fish).

Discus Eyes. The eyes of a discus should be brightly colored.  Many people prefer the bright red colored eyes, but you'll find  some that are orangish or amber. On most strains, a stress  bar will run through the discus' eye, and that can show on and  off, but if a discus has dark eyes consistantly, chances are  it's in bad health. If it's body is also dark and it's fins are clamped,  that's a double whammy and that fish should be avoided.  It could have some bacterial or parasitic problems.  Also, try to get discus fish with small eyes. Their eyes  will grow even when their bodies do not. A discus with  very large eyes in proportion to the height of it's head  usually hasn't eaten well for awhile or sometime during it's  juvenile years. Take a look at the first photo.  A good rule thumb regarding eye size, is to keep in  mind is that if you were to measure the height of the head  through the eyes, the height should be roughly 7 eyes tall.

 

Shape. Discus should be fairly round fish. In the discus hobby,  oftentimes you'll hear "football shape" - that's because the  body isn't round, but instead enlongated. Don't let the shape  of the fins conceal an unround body. Very young discus are  not round, but as they grow out and if they are properly cared  for, they will 'round out' (unless they have not been carefully bred).  Some of the breeders in Asia are producing very high bodied fish,  so these will not be as round.  Also when you look at a discus fish straight on, the body  should seem thick.