Fortaleza Brazil , SD & Durban poison

I strongly suggest you start from scratch with these if you're going to attempt to save them. I saw that you received them in this condition so you don't really know what caused this deficiency. Get new cubes(Rockwool), clone powder or gel and gently remove the old cubes as to not damage any root growth (if any), re dip the cuttings if you don't see growth or hardly any growth then replant in your new wool cubes. I recommend you don't soak the cubes either as they hold a lot of water and will easily drown young plants. Start off with minimal nutrients, mainly root inhibitors only and crank your rH up. I hope this helps.

I think these things are past saving, my friend. Sorry. My advice is to get new cuttings (this time with roots) or get some seeds and start from scratch. You've given them nutrients, but do not need to give them anything - cuttings just need rooting hormone at the point you put them into the rockwool, then allow them root for a couple of weeks before given them any food. Keep them under a plastic lid (e.g. coke bottle) to keep the humidity really high, chop off all the leaves except the top sets, and cut the tips of any remaining leaves to reduce transpiration (which would otherwise dry out the cutting). I even think it's better to keep them in the dark than full light, so long as your temperatures are in the right range.

Should I cover the cubes or tray so not to get light and make holes for the stems? You don't have to cover the cubes but you can do. I would wait to put them in the clay pebbles (or whatever you're using with your hydro system) until the roots have taken hold a little more, but you can transplant them earlier if you're having difficulties with watering. The roots are 4/6 inches long, how much watering should I be doing if humidity is being controlled at 75? Water them whenever they need it. You want the rockwool to be moist, not dry or soaking wet. How wet should the blocks be? Wetter than they are now - the ones in your photos look really dry! Give them a good watering and then wait for the plants to suck up >50% of it before you do the next one. How strong b52 and sensi grow should I use per 1L? 1ml Grow and 2ml B52 per litre of water according to the instructions - but I would go with half of that on the first feed. It also says you should use Micro and Bloom at 1ml each - you can do what you like, but keep an eye out for deficiencies that may appear as these things are usually formulated by the makers so that you need to buy the whole collection. Good luck, and good job bringing them back from the dead so far! :)