nutrients in fox farms soil

I’m starting 4th week of veg and I’m doing 4 sour diesel and 4 Durban poison in ff soil+perlite using ff dozen.I started 1/2 strength nutes week 2 and ph’d every time.ppm never over 1100.my runoff was 3800ppm.Was adding a tsp of Epsom salts to every 5 gallon cause this the runoff ph was 6.3.And...