Hi, The water is a little too warm - 78 degrees fahrenheit would be good. How do you regulate the temperature in his tank? If you are depending on the air in your office, when you are off work, they may turn off the air conditioning and heat, so his water temperature may be a lot colder or a lot hotter. This would effect his health negatively. Betta fish need an even, consistent water temperature and no drafts of air.
Do you mean you only feed him once a week? If so, then you are starving him. Also, only betta bite pellets and a few freeze-dried bloodworms may constipate him because he needs a little more variety in his diet. This may be why his water is crystal clear with only changing the water twice a week if you have a tiny desktop container. How much water is in his container?