The site is tanking but no manual penalty message

Selected answers from the Dumb SEO Questions Facebook & G+ community.

• 
  Jim Munro: This is not the problem but you might as well work towards getting it better. Your robots.txt will be understood by some bots but not all. Cut and paste this and leave a couple of blank lines after "Disallow:(space)(space)"
• 
  Jim Munro: User-agent: * Disallow:
• 
  Neil Cheesman: Space OR linespace?
• 
  Neil Cheesman: so... copy this... User-agent: * Disallow:
• 
  Neil Cheesman: and space or linespace after disallow?
• 
  Jim Munro: Yes. Both I think
• 
  Jim Munro: Note the capitalisation.
• 
  Jim Munro: I put two spaces after "Disallow:" followed by a couple of blank lines.
• 
  Neil Cheesman: What does this do? Allow: /
• 
  Jim Munro: It`s a bastardisation introduced by Google. googlebot knows what it means.
• 
  Neil Cheesman: okay... and I have amended the robots.txt
• 
  Neil Cheesman: Tonight, the homepage seems to have stayed at around 168 for a couple of hours and not gone back into omitted...
• 
  Neil Cheesman: and today dropped back into omitted results for "pet portraits"
• 
  Jim Munro: Are you going to fix this? I would, even if it is just a home page with the main site`s menu on it. There are some links pointing to http://blog.finepetportraits.co.uk/
• 
  Jim Munro: Have you changed the site since 19th March? http://webcache.googleusercontent.com/search?q=cache:ypEZY_QNkFIJ:www.finepetportraits.co.uk/kolbakur/&num=1&hl=en&gl=au&strip=0&vwsrc=0 https://www.finepetportraits.co.uk/kolbakur/