Why doesn't my milk every coagulate when it should? Caerphilly

[meyerandray]

I am attempting a caerphilly today, thanks to some posts by JeffHamm. (this is my 3rd cheese attempt)
I have put in the rennet in, and was checking the floculation time (I saw online when a glass bowl won't spin freely on top of the milk, that is your floculation time??) which I will then multiply by 4.  JeffHamm's was 16 minutes, and after 18 minutes I noticed my bowl spins just as freely as it did 18 min ago.  I did something that I am sure is awful at 19 minutes and 30 seconds...I added another small amount of rennet.  By 24 minutes I had floculation.  Just to understand how awful what I did was, could anyone please explain?  Also, should I be using a little more rennet than I have been?  For 8 liters of milk I have been using 1/2 tsp liquid rennet.  With goal cut times at 45 min for my first two cheese attempts, I actually was ready to cut at 1hr15min, so it isn't just this time that things seem to take too long to coagulate.  Any suggestions?

[linuxboy]

Increase rennet amount to at least 3/4 tsp.

[meyerandray]

Thanks again linuxboy!

[WovenMeadows]

One time, I was working with about 8 gallons of milk spread out into two pots - one pot coagulated, the other didn't. Not sure why. Added more rennet to the second and proceeded as usual (albeit now a staggered process), and as far as I could tell the cheese turned out okay (it was an Edam, IIRC).