Dramatic Drop in our best keyword - no changes for other keywords

We have a fairly new (16 months) ecommerce site and just recently working on SEO and committed to posting regular blog articles. We were seeing a steady increase in ranking for all keywords including a broad keyword that has 200K monthly searches. Over the last 90 days we moved from outside the top 100 to page 2 for this high volume keyword. Then suddenly about 10 days ago this high volume keyword took a nose dive and we are now sitting on page 14. All other keywords ranking have been remained steady with many others maintaining inside the top 5-10. Any clues as to what may have caused this one keyword to drop so dramatically? I cannot find any insight as to why in google search console.

www.koifishusa

Keyword: Koi Fish