Difference in ppms? Slurry vs RO.

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So I have black widow, gorilla glue #4, and zkittles. I have a few of each and want to go into flowering. I use fox farms trio and don't want to add any yet because I have a vivosun ppm/tds meter (more on that later) and I started testing some pots out. I repotted all my plants from 5 gal airpots to 7 gal fabric pots about 21 days ago using fox farms ocean mix for the soil. When I took ppm readings last night. I dug down 2-3 inches on the left side, right side (outer edges) and also the center by the mainstem. Got a 1:1 ratio of distilled water and soil slurry mix. My ppm number would consistently be for example 240 on the left, mid 300s in center and low 400s on tge right side. All seems good and it would be telling me that its time to feed. However, I know the fabric pots can possible give false readings on run off. So what I did was watered each plant with tap water and got ppm readings from the runoff aswell. All my run offs were at 1220-1250 besides for 1 plant so far that was at 2100. So my question is, should I wait for the plants to use up more of the nutes in the ocean mix soil before flipping or flush, flip them to flower and start feeding. I'm assuming that my soil still has sufficient nutes on top, and my root zone is pulling them out hence the lower ppms at the root zone. Is this thinking correct? Should I get a better ppm meter? I can't remember the ec numbers. My ph is hovering between 6.7 and 7.1. I will recalibrate my ph meter just to make sure however, I figure if those readings still come to that (measuring ph from the runoff only) i should start phing down to 6.5 and start watering with that aswell. Also I forgot to check my ppm of my tap water. I will do that tonight. I believe you just measure ppms in tap and then subtract that from runoff numbers? Not new to growing, but still trying to get a handle on my nutes. Running a x2 4x4 tents, and a 5x5 tent. Vipar 1000w in each 4x4. And a spider farmer se1000w in my 5x5. Water about 1/2-3/4 gallon every 4-5 days.
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