First time growing in years, and I'm unsure and don't want to do the wrong thing

Burning from over feeding........feeding too much or too often.....or both. In soil, a schedule of feed/plain water/plain water/feed/plain water/plain water/feed...... works well in my experience. There seems to be a common thread on this site with people using your chosen fertilizer brand.......problems.

Looks like a PH swing to me. In soil I do not alter the PH of the water, I let it do its own thing. Good Luck!