Slow develope on Coco/Clay

Yes you should give them some base nutrients+ calmag (important with led even more so in coco swallows up lots of calmag) with young plants it can be challenging feeding the right amount with tap water, guess your tapwater is already at 0.6 meaning it already contains lots of stuff, good and bad. A good one to work straight away with would be around 0.2-0.3EC have the same issue with my tap water, it’s recommended to go with a reverse osmosis system clearing the water to nearly 0.0 and start from there with your nutrients. I usually start feeding when they develop their first set of leaves and like do give foliar sprays at low dosing( around 0.3 EC), so the not so developed roots at this point don’t have to work so hard and can concentrate more on development rather than nutrient absorption at this time