Well
MangTheRooster,
Your rooster could be having several things that are causing him not to feel his best.
Diet:
He could be lacking in vitamins and minerals, especially if he eats a lot of corn and rice. He should be eating some 18% protein grower feed, or a higher protein feed. Otherwise, you'll have to balance his meals. Make sure he eats enough protein, vegetables, fruit, and carbohydrates, like the corn and rice. A vitamin supplement like Nutri Drench for poultry, would be good for him. A rooster that is out running around all day has to eat every one to two hours. They burn a lot of energy. But, your rooster lives inside your house, is that right?
Environment:
Environment is another thing that affects the health of chickens. They need sunshine and exercise, and the company of other chickens. They will get depressed if they do not have a natural environment. As a result they have a low appetite. Without proper nutrients their immune system can weaken. They can get sick easily.
It doesn't sound like he has any serious problems with his general health, according to your answers.
However, a clear poop (urine), is another indicator of a digestive problem. This could be due to his diet of corn and rice, infection, or his crop not emptying properly.
First thing in the morning, feel his crop. It should be flat, empty. If it has food in it, that is not good. Let us know if his crop doesn't empty over night.
Try feeding your rooster some scrambled egg, a table spoon of diced, cooked meat, some salmon or some other protein. This may perk him up. Also, feed him some fresh greens like kale, mustard or turnip tops, etc. Some thinly slice fresh apple or grape is good for him too.
You should also take a sample of his poop to a vet. Have them run a fecal float test. This will show if he has any internal parasites, like worms. A fecal float test runs from $10 - $20.
Let us know if any new symptoms show up.
These are my thoughts on your rooster's issue. I hope I have been helpful.
God Bless