The herbs in my tower are dying, what am I missing?

I bought these herbs about a week ago. They were grown in soil and I transferred them to my hydrotower. They looked fine for the first few days, the basil especially did really well. But they started to yellow and get stressed. It looks like the cilantro bolted almost immediately. They parsley has had a really hard time.

EC & Ph Measurements:

EC has mostly been about 1.5. It's gotten as high as 2.11 and as low as 1.35, but tends to hover in the middle. Ph on the other hand fights me daily! It wants to sit at 6.5. I add pH down to get it to 5.9, and the next morning, it's right back up to 6.5.

What I use:

• Nutrients: VIVOSUN Liquid Nutrients Base A & B Bundle
• Lights: Barrina 4FT T8 Plant Grow Light, 252W(6 x 42W, 1400W Equivalent), Full Spectrum, LED
• PH Down: General Hydroponics pH Control Kit
• Water Cycle: Started with 15 on, 30 off for maybe 5 days. For the past 3 days it's been 10 on 10 off because I thought it might help them. But they've continued to decline.

Hypothesis:

• Maybe I'm missing calcium nitrate and epsom salt? I thought the nutrient solution I bought was all I needed, but clearly all my plants are dying.
• Maybe the pH jumps are bothering the plant and I need to switch to phosphoric acid? I heard general hydroponics ph down has citric acid which results in this quick ph swings.

Your advice is so appreciated! 🙂

Edit: added water cycle details.