Yellow streak, no blotches, on young plant

Here's a picture:



I'm growing on coir, my nutrient medium pH is 6.7-6.8, but my soil pH meter shows a reading of 7-8 for some reason, so maybe that's the culprit? I don't know, the other plant, which is on the same medium made at the same time, and being fed with the same nutrient water, looks fine.

Any ideas on what's wrong? Will I need to flush?

not sure but if mine i would let it grow up a little bit and see if it spreads, other then that the rest of it looks good and if you are growing in same everything, give it some time and flush it later if need fit, dont over care for them that was my first mistake, remember they are a weed and can take some abuse