Salt buildup with biobizz fertilizers in biobizz lightmix soil, runoff EC grows after each plain watering. Each one takes 6 days to dry. Help

One easier option for flushing is using plan water then once its all done a weak feed, adding in a product called a wetting agent can also help the water reduce its surface tension and flow though the pot. If and when I flush I always do it slowly like a heavy rain this allows the water time to trickle though the medium and soak in vs dumping a big amount on top and then it compacts the medium or finds a easy way out and it all goes that way like a river vs though the rest of the pot. I use something called a sprayer and you just pump it up and water. I have a feeling some of the medium might be compacted and the first flush did not soak though some of it and that's why the EC spiked back up as it has time to soak after the first few flushes. Plants are looking good though and this might be part of end of life cycle, the purpleing on the top leaves are indicting of that. I think you should be ok with just water or weak feeds for the rest of its life. Congrats on the grow! Good Luck!