What's the easiest way to tell if slight leaf...

Hi there! If your plant tends to be lime green or pale all over, even though the leaves appear healthy without stripes or spots, then it's a Nitrogen deficiency. If your leaves are clawed and have a deep dark green, then it's a Nitrogen abuse/burn. If your issue only concerns the highest leaves, then it could be a light-burn. If your issue only concerns the new growth, then it could be an Iron deficiency. From what I see in your last pictures, this looks more like a deficiency. In every scenario, wrong pH can be involved. I'd recommend to re-calibrate your tools and double check your pH. Hope this helps, keep us up-to-date so we can help you in parameters adjustments, and happy growing!