No, no, no. Do not do this. Where do people get this advice? First, baking soda (sodium bicarbonate) is for the most part, insoluble in water. It is going to burn the shit out of your roots not to mention what the excess Na (sodium) will do.. Second, the vinegar is converted to acetate when you put that into water. Acetate is not good for plants. End of story. Buy yourself some pH up and down. It'll be anywhere from $20-$30 depending on the brand. That's nothing.
Yes, it is normal for the pH to go down. Some people said the stabilize the pH first before adding the nutrients. That's a waste of pH down, if you ask me. Most nutes are already balanced with buffers to naturally take the pH down to a reasonable region. Then you check it and adjust accordingly. Most of the time you will just have to raise it (like in your scenario) just a little. If you balance it first (which I have tried), it seems to take it too far down and then it's a bitch to try and readjust it because you will be adding quite a bit more pH up, and then that takes a while to stabilize in the solution. It becomes a pain. Just add nutes, and adjust if necessary. And yes, it's 100% normal for the pH to go down, even past the point at which you were aiming for. Hope this helps.
