well hell if there is gnats flying around you must have gnats! and they are coming from that soil. if you dont get rid of them you open your self up for other problems like wilt fungi. suggested treatments from the bible are the following sprays; vectrobac, gnatrol, and bactimos.
your temp sensor should be next to your top cola, if ur at 80 degrees at the base of ur plant you are to hot, your problem is probably a combination of heat stress and gnats, if fact now i am almost sure of it.
good luck