Keeping up with decay rate
I'm on the highest pace available on the settings (50 XP / day) But I'm spending the whole 50 just to keep up with the strength decay. I am only making progress if I put in about 80-100 XP each day. I don't mind doing the extra and the review is helpful, but I can't help wondering if I am doing something wrong.
No, you're not doing anything wrong. I usually start up the day with a couple practice lessons, do a few learning lessons, and then keep practicing after that. Strengthening skills before they get weak can slow down the decay rate, in other words, strengthening strengthened skills.
In addition, you will lose strength faster if you tend to hover over the words a lot. You might find more about that here.
I hope this helps, and good luck on your learning! =)
The strength decay rate will decrease if you get 50 xp per day while keeping completed lessons gold. I went through the Spanish tree like that, and sometimes I would spend a couple days in a row just reviewing, but the decay rate for each lesson would eventually decrease every time. This is assuming the developers haven't changed the system since then and the German course isn't very different, of course.
Duolingo uses a spaced repetition approach. It shows you things you've learned at times that will most help them stick in your head. If you keep the tree gold, you'll find it works really well. Sometimes that means you don't make any progress through the tree for a while - that's fine.
Duolingo takes account of how long it takes you to answer the question, and it takes account of whether or not you "peek" - whether or not you hold the mouse over a word to see what it means. When you can answer the questions quickly and without peeking, the skills will decay more slowly.
After you've strengthened the skills a few times, they'll start decaying more slowly, and then you'll be able to get further through the tree.