I thought the tarn would be easy to miss if you don't know what you're looking for - there are no obvious markings. It is on the uphill side of the track, after the start of the track being marked by posts and cairns (it seemed like we walked for quite a ways on mainly rock scree - maybe 30min?). You can't see the tarn from the track (there might be glimpses, but I missed them), but its not far off the track - maybe 50m. I noticed that just before we got to it we went through a bit of a dip, like a dry creek bed.
Sorry if that's not very helpful!

Hopefully others can describe the location better than I can!