P deficiency but what else?

If you are at 4ml/l of the grow micro bloom then that is about max dose. So I don’t think an increase in your base nutes is needed. If you aren’t adding a pk boost them maybe do that. Big bud by advanced nutrients is very good and will go well with your g/m/b. Is the stalk and branches striped purple? Personally I’d grab a small bottle of big bud. Is the gmb ph perfect? As you won’t need to worry about ph if so Hope this helps

I think you could turn up the TDS you are feeding it with. Just make sure to adjust pH to ~6.5. I think you could aim closer to 800 ppm.