Is it a nute toxicity?

could be shedding them? really depends on what you've added since the beginning. it's not wise to switch products, but it doesn't neccessarily mean doom and gloom. if it uses same ingedients, but in different proportions, you should be fine... otherwise you'd have to consider various chemical reactions that may take place with the mix of products and brands. More likely a deficiency and mobile? but, couldjust be getting rid of an old leaf if the problem is 100% isolated to 2 leaves. i'd assume the tablet just ups P? again, as long as ppm of P with what you've been adding doesn't go too high, that's fine.