Premium coco, worm castings and perlite, second week of auto growth, very slow growth and runoff is at 1.8 ec! why? Can drying cause this ?

This isn't soilless, so 1.8EC may or may not be concerning. Worm castings and other similar sources of nutrients often have components that need to be broken down by microbes before it can enter the plant. when this happens, You have an artificially high EC relative to what can enter the plant. worm castings aren't a complete diet, so if you haven't fed, that could also be part of slow growth. From plagron premium coco spec sheet - EC 0.09 – 0.14 So, it comes with zero nutrition in it. Because you used worm castings, you need to figure out what that adds and supplement it with a proper and consistent fertilization. You really shouldn't try to make a hybrid substrate. Either amend it with a more complete diet or just go soilless and provide 100% through fertilization with a religious 10% or more runoff. This skips the trial and error of what you are about to go through. 100% coco needs perlite. I'd wager worm castings make it even heavier? So, also start adding 2:1 perlite (33% perlite relative to coco). Coco on its own does not provide an optimal gas mixture around roots. did it wilt? if not, it didn't 'dry too much.' A normal wet-dry cycle is fine and will never hurt your plant. If you have a tiny plant in a huge pot, you could run into problems in this regard. One of the many reasons never to put a tiny plant in a huge pot, lol. if you do things that shoot yourself in the foot, you'll have endless problems. gardening should be easy. If it takes anything more than subtle formula shifts, most likely you are the cause of your frustrations.