... 79 is A-OK Spiffy, no worries there,... procedurally you did nothing wrong! That coco might be the culprit,.. my understanding is, the final prep' by the makers can be a Ca + Mg (?) buffering rinse to try and load up the coco ahead of time, so it releases readily instead of hogging it, and drive out the last of the Na and extra K,.. When you can, look up cation exchange capacity, CEC, and see what the deal is with that, and why coco is unusual,... if ever you need to flush, you must do it differently from true soil,... use RO/Di water, with 150ppm of Ca-Mg, plus 150ppm of appropriate nutes, pH to 6.0,.....
yup , hard knocks learns ya quick, but better still to avoid, especially with seed prices as they are!
.... and good investments, to that effect: a TDS or EC meter, and pH meter (you have already, yes?), and an Accurate 8 soil pH probe, for direct in-pot measurements! .. basic TDS is cheap, under $20, and the A8 can be had (amazon) for about $55,... the TDS/EC will show you exactly how strong the feed solution is, you can't just go by fractional dilution and be accurate, since each nute has different NPK numbers, plus all the other things that go in (ca-Mg, Si-- very recommended!.... humic-fulvics, etc.,...)... in this way with coco, you have to think hydro in your head, more than soil,... the probe will allow you to closely monitor the coco as grow progresses and changes,... the TDS can test the run-off for nute load, helping you avoid big, damaging, pH f'ing build-ups,...
... point is-- prevention,...adjusting your inputs before hand goe a million miles toward preventing TARFU situations, and the beating that fixing is!
