I love it when answers come to me through other peoples posts!
I had wondered about the payouts on posts decreasing. My first post to get any traction landed a $3 payout on its first day.
Just 5 days later it down to almost $2
I didn't have a clue that is was related to the value of steem and steem dollars. I had thought it was related to my vote power being close to 0%, so I stopped upvoting so much these last 2 days.
I can upvote again without worry =)
Payouts can also go down because the rewards pool is shrinking. It's usually a combination of the value of the currency and the size of the rewards pool. You can check your voting power by entering your user name here: https://steemnow.com/