I've just started developing two films which I've been shooting all of last month.

Then I drop a piece of film to test the fixer and it goes clear with agitation in 10 seconds.

The developer I mix myself, but I'm using fixer from a photo club which usually was supplied as working solution.

I usually don't agitate fixer when I test it, but it seems like a very fast time to fix. I don't want to end up with clean negs or no shadow detail and I don't have any other fixer now... and it would take a while to get. (a week)

How would you adjust to working concentration? Or am I overthinking this?