First Grow - 4L Pots - Jack & Critical

looks like you had a nitrogen abundance for sure! Flushing was a good choice. Make sure to start feeding with a lower (very low) dose of nitrogen after the flush BUT you have also flushed all the other nutrients than nitrogen. Meaning: Leaves turning yellow after the flush would be quite a fast reaction (from nitrogen abundance to nitrogen deficiency) Its more likely that you have washed out all of the magnesium and the plant suffers from a magnesium deficiency. (Symptoms are almost the same as nitrogen deficiency) I would recommend adding some extra CalMag + feeding with half amount of nitrogen that you've used before. If all the leaves turn pale green (although you've been feeding extra CalMag) you can consider raising the amount of nitrogen again until you've found the sweet spot for nitrogen.