i have used small rockwool cubes in the past for cuttings and had great success , but there is a little bit of prep required before using rockwool. During the manufacturing process to make rockwool some residues can be left in the finished product and it must be leached before use . i put my slab
or cubes of rockwool in the laundry sink and pour several litres of boiling water through the cubes to leach any nasty residuals from the cubes before using. After rinsing the cubes in lukewarm water I make a 50/50 mix of perlite and vermiculite and make a bed of this in my seedling tray. I saturate this with a very weak veg solution and then place my rockwool into this mix so that the cubes are approximately halfway buried into the mix. Poke a hole into the cube , pop you seed inside , push a little bit of the rockwool over the top of the seed so that it is covered from the light . Put a humidity dome over the top of your tray and dont add any more water until the seeds sprout . Only add water to the perlite / vermiculite mix and not the rockwool cube to encourage the roots to search for the water. A ph of 6.0 should be fine for the water . No nutes until roots penetrate the perlite/vermiculite mix and even then 1/4 is more than enough. Dont give up yet .