"Normal range" is subjective. Its plant and stage of growth dependant.
You didnt mention how big or what stage your plants are at but 773PPM seems high since I can see the base of one of the plants and it seems fairly small and untrained?
Im currently running about 550-600PPM in my resevoirs and I'll be flipping in about 2 days. I expect to get up to about 1000-1200PPM at peak flowering.
Test every day and the results will tell you if your in the correct range.
You want you PPM to stay steady or slightly drop/lower over a few days while your pH should slowly and slighly rise. That means your plant is drinking water and uptaking nutrients at about the same rate so the concentration (PPM) stays the same.
If PPM/EC goes up, then you've got too much nutrients on there and so its drinking eater faster than its uptaking the nutrients causing the concentration (PPM) to go up. If PPM/EC is dropping then you need to feed more.