Leaf problems and dying flower on orchid

[orchnewbie]

Hi All,

I was at my local nursery a few weeks back and fell in love with an orchid and decided to buy one.

I'm very new to orchid ownership and of course I have tried to do some research on how to care for an orchid. Keeping temperatures warm and humid, fertilise once a week and water when the roots look silvery. I also read that repotting when blooming isn't advised. The orchid has since bloomed 3 new flowers and been healthy up until now.

In the last couple of days my orchid has changed:

The leaves seem to have some rough "scrapings" with a difference in colour:




One leaf is starting to look really yellow!






One of the flowers has drooped and that flower stem has turned yellow.



I'm wondering what I have done wrong. He's an absolutely gorgeous plant I would really like to save him if possible. I really would appreciate some help and advice.

Thanks very much