Sorry for the update delay; fortunately, the plants are still alive. I discovered that the dropper I was using for fertilizers was incorrectly calibrated, so I've been giving only half of the intended amount of fertilizer until now. To help them recover at least somewhat, this week and the next, I plan to increase the doses. I've also adjusted the pH as you suggested; I hope they will bounce back.
@BobMassone, sorry for the late reply. I wouldn't add more fertilizer sooner than you normally would have just to lower the pH. Some nutrients will become more available to the plant at lower pH so you would probably risk nutrient burn if you added more.
@MasonKrae, No, honestly, I read on the internet that the pH should be between 6.5 and 7, so I've kept it around 6.8, except when I use fertilizers that self-adjust to 6.5. Do you think it's a good idea to re-fertilize by lowering the pH, even though I fertilized two days ago? Thank you very much for your help.🙏