Looked at it for 1-2 minutes and here is some spontaneous feedback/advice how you could improve some things without having to do a major overhaul.
use white background, not black
If you want to put "Proteinhaltiges Nahrungsergänzungsmittel und viel mehr..." centered, really center it. Right now it is set more to the right instead of centered.
Used "Spirulina" a lot of times in the navigation bar
maybe just write "Für Tiere" "Zum Abnehmen" "Muskelaufbau" "Spirulina kaufen" to reduce the width of the navigation bar. Then you can increase the boldness of the text there a little bit and can increase the kerning a bit to fill the width again
"Suche" button is too bright. Chose a darker green or use the dark grey color from the navigation bar
To be honest you could just remove the navigation at the right alltogether. Then the "TOP SELLER" and facebook thing would be more visible.
But if you do not want to do that:
Use a sans-serif font for the navigation list at the right (You can just use the same font as for the content text)
Maybe make some hover effect for it so it is more clearly visible what the user is hovering over / selecting
Put "Kontakt, Impressum, Datenschutz" in the footer instead of the nav at the right
Content:
Advertisment banner of "Terra elements" is not centered, looks a bit off because it is set more the the left
Decrease the size of the questions like "Ist Spirulina wirklich etwas für mich?". Put it at 24px instead of 36px. Also increase the distance between the "index"(list of the questions at the start) and the first question.
The website-path(don't know the term in english) should be justified left, not right.
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just some spontaneous feedback/advice. Unfortunately don't really have time to check it in-depth.