(Bloomberg) While many active stock-pickers these days are worrying about money walking out of the door, Cathie Wood will soon have the opposite problem. Her firm, Ark Investment Management, could be getting too successful for its own good.Already in February, Ark’s small lineup of exchange-traded funds has added another $7 billion in assets. That’s on top of January’s roughly $8 billion flow, taking the money manager’s ETF assets to $58 billion.“Too much money” is not a phrase heard often on Wall Street, but for a thematic fund specialist like Ark, it could be a headache. The business Wood founded seven years ago invests in future-focused trends like genomics and robotics, and there are only so many stocks that fit the bill.As the cash continues to pour in, Ark already owns 10% or more of at least 24 companies, according to data compiled by Bloomberg. They include Invitae Corp., Cerus Corp., and CRISPR Therapeutics AG.“There is risk w