It seems like every 400 miles or so my chain is really loose and it needs to be tightened back up. I have already done it 3 times this year and it needs to be done again. I know everything is tight too. What is causing this?

 

There are a number of possible reasons. They depend on a couple of things. How old is your chain in mileage ? How has the chain been maintained ? How do you ride ? How far are you riding between the times that you have to adjust it ?

 

I had a old chain, so it just got a new one about 400 miles ago and it needs to be adjusted again. I ride easy to hard depending on if i am by myself or with my friends. Seems like 400-600 miles it needs to be adjusted.

 

With a new chain, they will stretch more often, just consider it as a break in period.
It will need to be adjusted a bit more often, but will eventually settle in.
Make sure your adjusting the chain correctly, don't be tempted to over tighten it to compensate for it loosening up quickly, as this will just make it stretch even more.
Make sure you adjust it at its tightest point between the front & rear sprockets, chains never stretch evenly, so check before you make adjustments.
Smooth takes offs & smooth gear changes & keeping the chain well lubed will also slow down the time between you having to adjust it. It will also extend its service life as well.