I have never heard of using baking soda for lowering PH; vinegar but that is only a temp fix. You would be better off getting a "starter kit" that has both PH up and down and the testing kit.
The plants look a little bunt to me; can be from the outside temp or your
lights are too low or maybe your nutes are too strong. Could also be a deficiency in a required
nutrient like cal/mag.
I am not familiar with the nutes you are using but you want to make sure if it is a two part you are using both parts according to the directions and that they are PH stable thus reducing the fluxuations.
What do the roots look like? Are they white or slimmy or is there an ordor? Remember the plants can tolerate a higher temperature if the nutes are kept cool. You can cool them down by purchasing a cooler but if you are like me and can't afford several hundred bucks, you can just freeze two liter bottles and plop them in the nutes mid-day to help cool them off.
Gotta run to work, help this helps.