I will go ahead an answer some of you questions here, but you might get more responses if you start your own thread and describe EVERYTHING you can. We as fish lovers, love to hear about it, can't get enough

Tank size, water temp, number and wattage of heaters, number, type, flowrate of filters, gravel, decor, water parameters ... things about you, what made you fall in love with Os, your personal experiences, etc. It would make for a good new thread!
As far as diet, variety is good, but a quality pellet or combination of quality pellets (Omega One, Hikari, etc) should be 80-90% of the diet. FD Brine Shrimp is loved, but when they are bigger, the powdery nature of it can be bad, in the same way flakes are bad. The Os will pop at the water, taking the chance of swallowing air, which can be quite bad for them in the long run. I finished off the last of my brine shrimp by giving the O the clumped pieces and the mollies the powdery mess. Krill is a great treat, but my O also makes a mess, he 'shells' the krill and spits out the outside part, eating the tender insides, though he will do that will pellets sometimes as well, he can be silly. The coloring ... Protein is changed into blacks and browns, Spirulina into blues, astaxanthin is for red, corn gluten meal/marigold/egg helps with yellow, green is blue and yellow underlying each other. A good pellet with have sources of each and give you the best overall color and health. You can also give them crickets, worms, etc. as treats, if you give them feeders you must quarantine for a month or have your own healthy tank of them, and use warm water fish, cold-water fish such as goldfish have too high of fat and some have nutrients in them that lessen the ability to absorb vitamins that are needed by our Os. --- my special note, FD Daphnia seems to cloud my molly tank
If you go to the photo section, you will see how fast my O grew over 5 weeks and the color change he is going through. In less than 2 months, he has grown about 3+". This is fast but still normal for a healthy, well-fed O in a big enough tank. Oscars, when kept healthy, will live well over 10 years and get over 12" long from nose to base of tail. If you have them in too small of a tank or poor water conditions, they will stunt, which shortens their life and can make them more susceptible to diseases.
There are a variety of things that can cause a young O to pass away. They could have been sick or weakened from recent multiple transfers from the farm to holding to the store to your house and the various major water quality changes that happen through this process ... puts them through shock. The ich can knock out a baby O quick, maybe stress? But others would give you better possibilities than I can.
You need to treat the ich a.s.a.p. ... some use high temps (87-90F) and aquarium salt (1 TBSP/5 Gal) on other sites and
claim good results, others use an ich medication and heat. Ich can be quite deadly if not taken care of and needs to be treated for at least 3-5 days after you see the last of it, even longer if your temp isn't high. Make sure it is ich (salt crystal like spots) ... otherwise it is a fungus and can be treated with melafix and/or pimafix ... I had this problem before, I have
heard some have used this to treat ich as well (of course with raised temps). But use others' recommendations for your treatment.
Usually out of a group of 3 Os, you will have one oddball left out. As they grow and demand territory, the odd one will get picked on more than 90% of the time until it dies or you move it to another tank. 6 is the recommended if not one or two, but you would need a 300+ gallon tank to give them the territorial space they would need when adults.
From your other posts I don't understand if you have an adult O in a 50 gallon, if Cloud has passed on (looks like the post that said that was earlier today and I know Os play dead), so exactly what and where are all your Os and other fish? Ages, color variants? More info the better.
If a moderator wants to take these posts out and place them in its own thread, that would be great, I think the responses will be better for
redsun