Personally I recommend using an accurite or similar thermometer to monitor the heat tape while the thermostat is running, it just gives me peace of mind to have a second reading on my heat tape. I have a small isolation (quarantine) rack that I use a Jump-Start on and I've found it can vary a little bit with how well it controls temp.

I also definitely recommend checking to see if your thermostat probe is still mounted securely in place, as if it drifted away from the tape it could allow spikes.

Lastly, I believe C Serpents use FlexWatt heat tape which I'm not a fan of, their racks are great, just the heat tape bothers me is all.

The THG tape that Pangea sells is WAY better in my opinion, and priced well too. In my experience it's more flexible, better constructed, and less likely to hot spot and will therefore heat more evenly.

I actually have just under 40 ft. of 6" THG tape on the way from Pangea right now for a new 9 high, 1/2/3 tub wide, combo rack I built, should be here Friday. I can't say enough about how much I like THG as a product and Pangea as a distributor.