Looks like BER to me.
Here's a link about it from NC State's extension office:
https://content.ces.ncsu.edu/blossom-end-rot-of-tomato-pepper-and-watermelon
I've been using multiple applications of Sevin. Which I'm not a fan of using in the vegetable garden, except in extreme circumstances like fire ants.
I'm going to try your borax method next time instead.
I still love to grow Mojo Frutegum, which is a BB7 derivative.
The plants have lots of purple tinge to the stems and leaves.
But of course, their bleeding calix is the icing on the cake.
Just to echo what everyone else has said...
I use the cheap Jump Start thermostat set to 80F (about 27C).
Your seeds will appreciate it and your mat should last longer too.
The hottest one I ever grew was a 7 pot Douglah from seeds I got from AJ Drew several years ago.
He sent me some of his Carolina Reaper pods around the same time, and I couldn't tell the difference between the two pungency-wise. :fireball:
I've bought from THP several times now, and have always been satisfied.
While there is always a chance for an unintended cross to appear with any seed vender, I have yet to have a problem with seeds from THP.
I'm using mine for backyard lighting too.
I love how it can be set up to turn on automatically at sundown so I don't have to keep adjusting it throughout the year, or reset it when the power goes off (like with old fashion timers).