I wouldn't use a premix thinking it's going to "fix" any issues... premixes typically cause another set of problems of their own and they're usually harder to fix. Looking at the photos you included, I'm not really sure what issue you think you got....the very slight yellowing on the leaf tips or the purple veins on the back of older leaves. Regardless neither are worth chasing after, your plants look pretty good and I would continue with whatever you are doing. If the leaf tips get worse maybe monitor your pH a little more closely or dial back your EC a hair, but again it's not that bad....pretty good really.