I think that it was really strange that in January when BTC went down all big cryptocurrency exchanges closed registration for new members and they opened it only when the price was low. Then at spring when the downtrend was broken(7000$) there were many news that cryptocurrency now will go up! But whales just made big shorts at 10 000 $and all the news said that cryptocurrency won't go up for along time and market went down to current position.
Concerning exchanges closing registrations,that's normal because the exchange platform can't handle infinite members because hosting limited performance etc..They had to close the registrations to expand their capacity of members by upgrading their servers.Thus,it's not really a manipulation from exchanges.However,whales are kind of manipulating the market we've seen this many times now a whale sold his coins and a huge wave of sells followed him.
But still by closing it they just helped crypto market not to get more money. I mean they closed registration(simultaneously!) exactly in that moment when the market turned around. It looks really strange. Maybe there were really has technical problems with registration new users but still I think that it wasn't the whole reason