You don't want to fertilize a plant that's struggling. How did the roots look when you unpotted them? How much are you watering?

Roots seemed ok, can’t remember too well. I was watering every other day (small amounts) but moisture meter is between moist (good) and wet (bad). maybe its that but the other geranium in the picture that is doing well has the same conditions.

Could maybe be over watering then. only recently got this moisture meter so going to leave watering until it says it needs it. Attached a picture of multiple plants in this bed - penstemon and astrantia. Also you can see geraniums either side of the circled bad one which are the same variety but doing much better; only a few yellow leaves. Could also be the variety as I also have three of the good picture from my last post and they are all looking very healthy.