i've seen better growth and color with alk 7-7.3 dKh yet i'd agree that low 8.x is fine too. like anything, take note of where your salt mixes at and keep consistent.
IMO, the issue is not the methods used, but the nutrient levels attained, and if you keep them very low, you may want alk in the 6.5-7.5 or 8 dKH range.