Patch on leaf

Possibly... Unfortunately, leaf symptoms are not discrete. So more than one thing can cause some chlorosis. Image search for a leaf symptom chart. The one i like has 'cervantes' name stamped on it. explains mobile vs immobile etc... Mulder's chart is something to glance over just to understnad the relationships between each individual nutrient molecule and how they impact the availability of other nutrient molecules ... antagonistic vs stimulative relationships... mostly they are antagonistic. When you have a very complicated set of symptoms, "mulder's chart" cna sometimes be useful if you track what you feed over time and familiar with your soil produts etc... Where it starts and how it progresses can help better diagnose, but even that is not always enough to be 100% confident. Soil has some unknowns, but familiarity with the product and keeping track of the fertilization you provide can further increase accuracy of diagnosis. Great thing here is that it looks to be slow moving, so there is a highly likely probabiliy of only a slightly out of balance cause behind it. I'd wait and see how it progresses before making any assumptions. Also, sometimes a leaf or two gets shed by the plant or has a blemish that doesn't spread or cuase major concern... Be certain before you react. Doing the wrong thing will only make it worse. You can do smart, non-intrusive things in the meantime, like check the pH -- pH of runoff or soil slurry is not super accurate as to what is in the medium, but anything gortesquely off or if it is trending in a specific direction over time would be bad signs. In this case i doubt it is a major pH issue, as that would usually cause a smorgasborg of symptoms because it has the potential to fuck with everything. Plus, first issues usually relates to calcium but calcium does not cause chlorosis... it causes reddish-orange-orrusty spots as symptoms for a deficiency. Good to form a baseline for what pH looks like when things are going well, because how you measure it almost always is an offset from reality. whether you test early runoff or late will make a difference in the reading. How much substrate you use in a slurry and how much and what ph the water you add to it for a slurry will shift the pH reading, too. So, don't overreact to an odd pH reading if the plant is 99% healthy. learn what is normal for a happy plant, then it can be useful to measure and compare in future. Have a set process and be as consistent as possible as far as how you take that measurement.