Hard to tell. It looks like potassium plus iron deficiency.
But I'm going more by your current tank description than the picture, comparing the conditions against times I've had similar setups. The pic is too small to see certain details, like pinholes. Some of the visible algae that may act as clues aren't reliable here, since they may be lingering from what sounds like a recent lighting downgrade. And judging nutrient levels by plant appearance is a bit more art than science anyway, especially when multiple deficiencies might be involved.