There's been a fair amount of talk about "decreasing volume" in the market. I don't see that as the problem with the SPYs and IWNs. I do see it possibly with the QQQQs. Here are the charts of the SPY, QQQQ and IWN with an exaggerated volume display. The horizontal line is a simple eyeballing of the recent rally's volume level with other volume levels.
I think what some people are missing is the China sell-off distorted volume readings in the market. Take a look for yourself.
I should add that I see plenty of other problems in the market -- namely that the economic preconditions to a solid rally aren't there. But it doesn't look like volume is an issue at this point.