You are going to continue to have issues specially in flower. Soil needs perlite for drainage and oxygen to the roots. I suspect your roots are suffocating. If you’re in California there are a plethora of places you can buy good growing soil. Not sure about the rose fertilizer. No experience. Hoping some others chime as im coming to a road block. I’m a relatively new grower as well. Honestly, if I were you, I’d go to Home Depot, buy a 10 gallon pot. If you’re able to source fox farm ocean forest soil get some
Of that and transplant to the bigger pot. Water with only h2o for 3 weeks. Not sure if you’re able to do that.