how to know when the price will go down? (i want to invest when the price goes down)... is there any site where i can deposit money then just instantly buy when it goes down to a specific amount? ex: when Ethereum's price decreases to $2xx, immediately purchase a lot...
Thats a standard limit order on an exchange. Kraken or Gdax would be the obvious ones for buying with usd etc. Poloniex for buying with btc.