Yellow leaf DwC hydro

More than 1 thing occurring. overall concentration is not all you have to worry about. Ratios of nutes are equally if not more important. Some nutes compete with each other and if one is too high the other gets locked out even if present in high enough quantities, otherwise. Some have stimulative effects on other nutes. E.g. adding more N generally means you need more Mg too. looks like N deficicny and maybe k-deficiency, but knowing how it progressed would help a lot. Since there's more than 1 symptom, lockout of some sort is possible (a nute too high or pH caused) in late flower you probably need 80-100ppm of nitrogen. This will heavily depend on heavily you fed it leading up to flower, too. unless your ppm readings are including tap water, the ppms contributed from fertilizer probably shouldn't be that high. 1.3-1.5 EC from fertilizer + what the tap adds to that is a better ballpark to start. plant dictates what it needs relative to all the local variables of your garden... follow that to make adjustments.

So many long term issues, no diary and so little information..........impossible to answer accurately.

What you're showing us didn't happen overnight. I suspect you've either been dealing with some drastic pH inconsistencies or maybe you're using a weak air pump. Was this recent tank change your first over the 9 weeks? There's a lot of possibilities and not enough info.