I have a small set of data that I need to fit a curve to  (see image).

[![enter image description here][1]][1]

The data came out of a simulation model for which I was stressing a parameter (filtration rate) then recording what happened to my variables (algae concentration and adult density). Now, I need to fit a curve to this, and I have to admit I never saw this kind of decline before. So, I would like some suggestions about how to fit a curve to this. It seems to me that a power law might be needed, but I have never worked with those before and am not sure how to go about it.

I've spent all day reading about power laws and trying to fit it on R but only managed to confuse myself, so any help will be highly appreciated.


  [1]: https://i.sstatic.net/w18Wt.jpg