Agreed with the abouve on cell builder NO open larve. In the past I was doing a bit of open and getting a 605 or so take, but they would tear them down in 3 days. Went to a class with Dave burns 2 weeks ago, and learned a new trick. sweep a darn lot of nurse bees into a nuc. about 5lbs worth only nurse bees sweept from brood nest... put your grafts in after they have set overnight. 2 frames of food, 1 pollen, 1 honey, and empty frame (for them to draw wax on so your cells are not covered) and one of capped brood if you got it. use that as a starter you can cycle 3 groups thru before the bees are too old.
This means you have 5 lbs of nurse bees with nothing to do but feed your grafts!... I grafted 50 cells last sat that way, and have 46 queen cells today
Ditch the water in your grafts.... just a flat single graft will work fine. if the larve forms a c its too old. slight curve and very tiny!.. for me the graft technique was fine, it was the cell builder I had to improve.