that is a big drop in your run off.... imo, that would be a signal to raise my nutes a bit... i would try bumping it up to 1100-1200 and see what the run off is...
that is one way to use the meter, If the run off comes out higher than what you put in, then i would lower the ppm's.... if it comes out way way lower like yours did, then i would increase the ppm's. But this method only works when the coco is fairly new, once the coco starts to decompose then it will skyrocket the ppm's of your run off and basicly give you false readings.
u can also use the meter to increase and decrease your nutes depending on what week of growth u are in as well as to check your tap water for quality.
organic nutes cant accurately be measured with the meter fyi