Baking soda can raise your kh. I think your light and no co2 is the problem. If it was me, I'd raise the light or dim it. Screen works good for dimming. Liquid co2 like excel or api co2 booster help with algae control also it will help your plants grow and out compete the algae. Start with adjusting light intensity and adding another source of co2.A little over 4 weeks. How do I raise my kH? and to what range? 6ish?