Total words percentage is going down.
After finishing my Spanish tree, my total word amount keeps going down. What can I do to stop this? I keep the tree up to date every day. I wish there was a list of instructions for Duolingo. Not the most user-friendly site.
The generic Strengthen skills button actually targets the weakest words and not skills. So multiple rounds of practice with that is an option. Weakened words you can find in the Words tab. If you click on Strength, the words will be sorted in order of increasing word strength.
One more thing. This is purely based on Duolingo's spaced repetition algorithm. If you are confident that you do recall all your words, you don't need to practice more just coz Duolingo says. But, it is good to have a regular practice schedule in plan when learning a new language (or any other subject for that matter).