There are a lot of factors to consider when cloning. Here are some pointers from my experience in addition to what you are doing already:
1) Take clones from the bottom of the plant - don't take the growth nodes at the top. This makes a huge difference in rooting time.
2) Don't take large clones. More plant = more energy needed to sustain it = less energy to develop roots. The clones need very little leaf matter to carry it over during the rooting process.
3) I find it works best to use a rockwool cube (the small ones) to help keep the plant stabilized.
4) When you take the clone, cut it with a clean scalpel at a 45 degree angle and immediately apply a rooting hormone. Then stick it in a cube.
3) Water with ph balanced water (slightly acidic) and a light vitamin B enriched solution (like Root Excellurator). No nutrients needed during rooting.
5) Keep the cubes moist, but not saturated. You want to promote root development by having the plant 'search' for water. Too much water and it will rot. I usually water a tray of about 100 clones once every 5-7 days.
6) Roots need a lot of O2 to develop. Aerate your water (filtered) with an air stone and again, don't overdo the watering. Most of the plants needed water will be absorbed through the leaves in your canopy anyhow (hence the high humidity).
7) Keep your light minimal. You are supporting root development, not growth. Clones only need a weak full spectrum bulb to get enough energy to develop the roots. I find a T5 about 3ft away is ideal.
8 ) Warm the roots with a heating mat to reduce rooting time. The heat directly applied to the rooting area (74-78 degrees) will promote root development and keep your dome humidity high.
9) Don't mess with them. I cant tell you how many times I ruined a perfectly good clone by pulling it to see if the roots were developed. When you see roots poking out the cubes, they are ready for the pull test.
Thats about all I have to share. I enjoy near 95% cloning success rate by following these steps with a variety of strains. Take what tidbits from my experiences that makes sense to you, and good luck!
