@ dodidoki
Thank you dodidoki for your infos.
[600 uS , every waterings, in winter 300 uS.Fertilizers are Peters Excel Ca+Mg and Peters Blossom Booster, in spring 3:1 and shifted to 1:1 gradually till fall.Water is rain water, measured conductivity about 50 uS here.I attached a pic, purpurata with 6 buds on one stem.]
If you use the Peters CalMag Grower when your conductivity is 600 µS the nitrogen content of your solution (which is the most important) would be around 90 ppm (mgr/L). In fact, the technical data sheet of this fertilizer mentions a conductivity of 1000 µS with a concentration of 1 gr/L or 150 mgr/L of nitrogen. This seems very high to me. Is a such high nitrogen content common among Cattleya producers?