When's my mother ready?

I watched a few videos online about how to create a mother SCOBY from scratch using the cultures from a couple bottles of GT kombucha. I went through the whole process today and have it sitting quietly waiting for my mother to form but I'm not sure how to tell when its done. I know its going to take a couple weeks but what do I look for to decide that its finished? I'm using a standard one gallon pickle jar, so do I measure the thickness of the SCOBY, or should I take periodic pH tests until the tea gets down to 3.0 and then call it done? Or follow some other method? In the videos they just say "ok, the mother SCOBY is done" but don't say how to determine that.

Thanks bunches!

I just taste it. It's easy to tell. It takes some time to create a SCOBY from bottled GT, but I've done it. Once you add the SCOBY to your crock of sweetened tea, a lot depends on the size of the crock. When your culture has grown to a layer that covers the entire surface of the liquid, and has a little thickness to it, you know it's doing fine!

Its doing good so far, the SCOBY covers the surface and is between 1/16th and 1/8th of an inch in thickness after just a week and there is a good deal of yeast sediment on the bottom. Its been crazy hot around here lately and our house absorbs heat, so my kitchen has been upper 70s to low 80s so my SCOBY is forming nicely. Once I get a chance I'll take a pic.

Here she is! This is about a week after starting the project. I think she is looking pretty good so far, no mold and no bugs or anything thanks to my paper towel cover.

1/4" thickness is average when it comes to purposely growing a mother. Future generations typically improve, and around #3 or 4 you really say WOW!!

So how long can I save a SCOBY in the fridge? I'm thinking I'll keep one as a spare in case something ever goes wrong, that way I won't have to start over from scratch like this.