I have had problems with flower set over the past few weeks. The temperature in my conservatory has been so high at times that the pollen has failed to set.
Never mind! … there are plenty of new flowers on the way which should set later in the season.
I’ve noticed that the amount of food, the nutrient strength, can be reduced a little. Owing to the size of Minibel variety, it doesn’t need as much feeding to grow to full size as larger plants do.
I suggest that at this stage, the rockwool is given a flush-through with plain water (pH adjusted) once each week. Also, if you can, keep the water level at a maximum of one centimeter to avoid the roots becoming too saturated – in other words… best not to have the rookwool in a constant 2 centimeters of water, otherwise it may affect the roots.