One of my plants has yellow marks on the leaves an...

Yh I think it might be dry spots it’s not ph I checked the run off it’s at 6.4 I don’t have a tds meter at min buts it been getting same feed as the rest like I said 4 are dark green slightly n toxicity and then this one yellowing and new growth is bright yellow and the other 16 are growing perfect it’s pretty strange must be difference in pheno

Doesnt look like nitrogen overload. Is it near middle and top of plant? Fabric planters? If so, maybe some dry spots in your root zone. Gets hard to wet the entire medium once roots have filled them good. You need to make sure you have 20 to 30 % running out the bottom after watering or feeding. Also need to check the first bit that comes out for ph and tds, make sure things arent going out of whack on you. Cheers friend