Nothing left to strengthen
I managed to strengthen all my topics so that all the buttons turned from a colour to orange. I have done this a few times then I practice weak skills until the buttons revert to a colour again. I have been practicing the weak skills for a week now and have just moved up to level 18 French expecting the buttons to ask me to strengthen a topic but they have stayed orange for a week now. Why is this? I do not feel that I am making progress and am getting a little bored. I use the app and have updated it but it is the same on Safari.
Translation in inmersion is a good practice to improve in vocabulary and writing skills, with the help of other people that correct your translations. And also, you have not finished your tree yet. You can also do revision of topics playing against the clock. Buy it in the shop. And when you finish your tree you can also do the reverse tree and try inverse translation. I hope my tips will be useful for you. That is all I know.
Thank you for your response. I use the iPad app for duo lingo and it doesn't have as much content as the site. Looking into it more today I see that I have finished my tree and have earned the trophy at level 18 but because I know that there are 25 levels I thought that the tree would keep refreshing with more difficult content. Using the 'Practice Weak Skills' at the bottom of the tree on the app is good for learning but I see now that I may need to use the actual site from now on if I wish to access more challenging content. I will also check out the inverse translation you mentioned. Thanks again!