This week, the ratings of three chemicals stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Tronox Ltd.’s (TROX) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Tronox produces and markets titanium dioxide. In Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth, TROX also gets F’s. At $23.95, the stock is below the 50-day moving average of $24.16. To get an in-depth look at TROX, get Portfolio Grader’s complete analysis of TROX stock.

Calgon Carbon Corporation (CCC) is having a tough week. The company’s rating falls from a C to a D. Calgon Carbon is engaged in products and services for purifying water and air. For a full analysis of CCC stock, visit Portfolio Grader.

Rockwood Holdings, Inc. (ROC) earns a D this week, falling from last week’s grade of C. Rockwood Holdings is a global developer, manufacturer and marketer of value-added specialty chemicals and advanced materials used for industrial and commercial purposes. The stock gets F’s in Earnings Growth, Earnings Surprise and Margin Growth. To get an in-depth look at ROC, get Portfolio Grader’s complete analysis of ROC stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.