The recent market pyrotechnics have lifted stock market volume. And that was good news for dark pools and lit venues alike. But the rising tide of volume did not lift all ships equally.

According to Rosenblatt Securities, trading in the dark pools increased 31.2 percent in August. More than 1.2 billion shares traded via dark venues, the second highest monthly figure after May 2010 (during which the infamous Flash Crash occurred). But the surge in volume still trailed the 46 percent surge at public exchanges--the NYSE, Nasdaq and others.

So what's going on?

The Financial Times notes that when volatility spikes and leads to more volume, many market participants place a premium on trade execution certainty. One expert told the paper: "Dark pool market share will come down when volatility in the market increases, because the urgency to trade increases too. Higher volatility means the potential cost of non-execution goes up."

The biggest declines in market share were in large block venues run by the likes of Liquidnet and Pipeline Trading. Market share also declined for internal pools run by Credit Suisse and Goldman Sachs. In contrast, the dark pools run by high-frequency trading market makers fared extremely well. Getco, one of the largest high-frequency market makers, saw market share increase nearly 50 percent. Knight Capital was another winner, as its market share rose 74 percent.

Institutions no doubt prize their trading options when the markets go haywire. The last thing they want are new rules that might alter the dynamics in ways that create more uncertainty.

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