What is it?

Those isolated pale/rusty spots don’t make me think “not enough Bio-Grow” straight away. The rest of the leaf looks reasonably healthy, and 1.5 ml/L tells us very little without knowing the soil, water and pH. At 25 days I’d avoid increasing nutrients just because of a few spots. First check whether the damage continues appearing on new growth. Also get that pH measurement sorted; nutrient availability can be the problem even when plenty is present in the soil. One extra thing I’d check is Ca/Mg, especially with very soft/RO water or an LED setup. Early calcium issues can produce scattered spots like these. But diagnose the trend, not one leaf; if new growth stays clean, I wouldn’t chase it with bottles.

Sometimes leaves get damaged for various reasons. When more than just a couple leaves are taking damage and it seems to be spreading and getting worse, then it is easier to read as a systemic deficiency. Closely observing your plants and doing inspections is very good. That is the first principal of having healthy plants, and you have that going on. Keep watching for what the plants are communicating. Right now they are saying, Ah, its nothing really, just a scrape. I'm still running the marathon.

Looking at the other pictures that doesn't appear they are overly pale maybe just slightly hungry, but nothing to be concerned with. The little marks look like scold marks from water droplets sitting on the leaves and the light being magnified by it. That wont heal just try to ignore those and of you get leaves wet try to shake them off. Sun scald can be avoided or minimized by watering first thing in morning. Higher chance of it causing damage watering later in the day .