The OP has not wormed him and does not know if he was wormed prior to her getting him 6 weeks ago. He is mature so Cocci was not a first guess as they are generally resistant by the time they are mature. Worms will cause a loss of appetite leading to watery poo, because they are not eating much...
Okay rooster booster doesn't look too promising. It is apparently intended as a "continuous use" preventative, not a cure once they are already infested. Safeguard is Fenbendazole also known as Panacur. Horse paste Panacur can be used as well if you can get the paste into them, the liquid drench...
Safeguard is a cattle or goat product, did you check that section or just the poultry section? Wazine can be used, but it does not cover as many varieties as Safeguard so it may or may not work on the type worms a bird has. I am not familiar with the rooster booster product any idea what the...
Do you have any safeguard or other wormers? Even on the coldest days mine were active and alert, something has him feeling weak and worms would be my first guess.