When in dout flush them out.6.4 or 6.5 is fine for soil.The soil act as a buffer so the ppms are a little low.Whats the run off PH at?What nutr are you feeding them?Flush them out and when dry feed them alittle stronger nutrs.Not alot more just a little more.They look like mind did till KP told me I wasnt feeding them enough nutrs.What kind of nutrs are you feeding them now?