Clones in unprepared rockwool

Hey Everyone, I received some clones recently and they have begun to look very sick; Ca and P deficiencies from the looks of it (or lockout specifically). The clones are in rockwool and we have been applying a nutrient solution of pH 6.0; a mixture of Floragrow, Floramicro, Florabloom, and Calimagic diluted in DI water (total ppm of 600). I thought that we might be experiencing lockout due to a low pH because the first nutrient solution we applied was 5.4, so I decided to flush the plants/rockwool. I tested the pH of the water that came out of the flush and the pH was 7.8. So now I'm thinking that the issue is that the pH was too high because the person from whom we received the clones did not prepare the rockwool cubes. Does anyone have any experience with retroactively preparing rockwool after the clones have been growing in it for a couple of weeks? Is flushing my plants with pH 5.5-6.0 water the best course of action? Thanks for any advice! This is my first grow so I really hope that I don't have these plants die on me.

 

Awesome, thanks so much! I will try your suggestions and see how it works out