Sept 15 was tax day. Companies withdrew money they had in the market to pay taxes. It is a regular occurrence every year, but this year it was a problem because

Sept 15 was tax day. Companies withdrew money they had in the market to pay taxes. It is a regular occurrence every year, but this year it was a problem because the FED tightened. They assumed 1 trillion would have been enough but now are looking for the correct amount buy adding money. They are still trying to figure it out.