I'm assuming this is a deficiency because it is showing up on the tomatoes in my existing grow bed as well as on the basil and sage in my new grow bed. Some leaves on my tomato plants are curling up and dying while others have small brown spots on them. The basil and sage in my new bed both have small brown (dead) spots on the leaves. (pictures attached)
I have recently added epsom salt and have buried a banana peal in my old bed where worms should be doing their work. My ph is right around 7.0 (maybe slightly above, but not much, though keeping ph down has taken work), and I have decent nitrates. The system is 600 gallons with goldfish, tilapia, perch and a catfish. My existing grow bed is 2.5'x3.5' and my new gb is 3.5'x4'. I also have a 20' pvc pipe loop where I grow greens.
Please offer any help you can on the plants as I've had problems last year too and am about to give up on some of these plants. Thanks.
Basil gets back spots, yellowing and leaves fall off when humidity is high. I usually see this outdoors in late summer with high temps and lots of rain. You could try a spray of baking soda. If indoors you may need a dehumidifier.
If the spots on your tomatoes aren't a deficiency, I can't say what it is. If your search deficiency on this site, you should eventually find a document describing deficiencies/symptoms.
To raise PH, I use calcium hydroxide and potassium bicarbonate, 50/50. Tomatoes need both.
I also add iron and if you search that topic on this site, you'll find a recommended dosage. I use about a gram per 3 weeks or so in 400 gallons - so about one third of that amount per week. See Bright agrotech on the subject also.
Epsom (magnesium) I add about 1.5 tablespoons every week or two.