Garlic punch dwc n dirty z

About 2 -3 weeks from seed here. Got scared once I saw the roots starting to brown a bit. But no smell and after calming down I came to the conclusion it's nute stain. I'm using great white shark so there's those good beni bac in there helping. I tried to keep the res temp down but once it started to have more roots in the res I didn't like the frozen water bottle trick . I started scooping a cup of solution out and putting it in the freezer to the point it just starts to ice up and I'd put it in the res and repeat. It helped get the temp down to more of a 68 instead of 73 with nothing Keeping it at about 300 ppm and 5.8-6 ph.