It's hard to say exactly. If you are referring to the yellowing then calcium, magnesium, iron and nitrogen are the most likely but if it's the newer leaves then it is more likely to be the immobile elements such as iron as the plant cannot move this to the new leaves. Magnesium is very mobile so if you have magnesium deficiency you should see improvements straight away simply by adding magnesium sulphate.
It is also possible that you have too much of one or more nutrients that is outcompeting something else. This is called nutrient antagonism.
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But perhaps you don't have enough co2 or too much light? Could be many things and different species may react differently to shortages or excesses.
Make changes slowly and one at a time if you want to pinpoint the exact problem or you could try adding a bit more of everything whilst reducing light and uptake. Just don't go overboard.
Good luck