Here I have three different different reasons that why the price of the altcoins goes down in.the week .
1) The ico attracted the people more , so few of the Bitcoiner sold the altcoin and invested in the ico , results into down price .
2) Increase in the price of the Bitcoin , so to complete the demand of the Bitcoin they sold the altcoins .
3) The big movement of the Bitcoin legalisation is going on in the whole world , currently many of the countries the new new news are coming and saying that Bitcoin will legalise soon , this made the increase in the demand of btc and many of the people bought Bitcoin .
So to go behind the Bitcoin and increase in demand made the down of the investment in the cryptocurremcy market mainly for the altcoins .
This reply covers the bases pretty well. I think the upcoming fork has lots of strong, big balance btc holders a little spooked. Which seems to be having a mixed and somewhat unpredictable affects on alt coins. Things will smooth out in August.