Yellowing Leaves on Plants

Hi all. Thanks in advance.

I just updated my garden with 25 yards of an organic soil mix. After putting this in my garden (much better than the lifeless sand I had in my North Florida garden), my plants were thriving like I've never seen. Now, I see some plants leaves are starting to turn yellow.

I am using an organic fish emulsion (non-pasteurized) for food, and I'm using less than the recommended dose and feeding every two weeks. I am not yet set up to make my own compost tea but that will soon happen. I just need to propagate more plants for making compost tea (I'll start doing this within a few weeks) and I always use less than recommend (fyi) fish emulsion. Even still, my tomato and other plant leaves are turning yellow.

I have a moisture meter that measures how wet or dry soil is, but it also measures pH. I flipped the switch to pH and the needle went to 8 or 9, which I know is not good - very alkaline. Given that my garden is heavily populated with all kinds of stuff, what is the best way to make the soil more acidic so that the pH falls in the neutral range of 6 to 7? I have not done a proper soil test yet - I've only used the meter I have that measures pH. I was thinking of maybe doing something that acts immediately so my plants do not languish unnecessarily, and then seeing what I can do longer term.

I don't think the leaves are turning yellow because of nitrogen issues, though I'm not entirely sure. I think it's more an alkaline / acid problem.

Any and all advice is welcome here. Thanks!!

Logan

Diluted vinegar and coffee grounds are what immediately come to mind. Pine needles and sulphur work as well, but take longer to break down. I've also known peat moss to be a recommendation, but I recently read that peat is no longer recommended...but I can't remember why. Perhaps someone else can chime in there.