ah, missed it's a slow release thing... that's the problem with those if not precisely mixed... and a one-size-fits-all doesn't really exist for all strains. Irrigate with a little extra runoff in that case... don't stop. Likely lasts till end, but do react if it improves.
i wouldn't try any aggressive flush, unless someone has experience where that helps... will cause a lot of negatives too. If things are developing seemingly well, don't rock the boat too much this late. more likely to cause more harm than good in many contexts. sticking to ph-only for a while is conservative and safe.