If you have a pH probe, get a shot glass and a cup, fill the shot glass with soil between the plant and the edge, put it in the cup, add a shot glass full of the water you use, and let sit about 5 min, then test the pH carefully (dont want to hit the meter on perlite)
Once you have a starting point of where the soil is, when you feed, feed a little high, 6.6 or so and recheck after a week or so, idea is to bring it back in slowly. Or, if it's way low, amending will be an option too..
I'm hoping your just on the lower edge.
If you can feel damp sticking your finger in to the first knuckle, your fine, if dry, then go ahead and start. I use the dry weight method, something you pick up with time.