Disk size keeps shrinking I am not a pro at Mac / OS X. But I know my way around.

I just installed OS X El Capitan. However when I first started up, my harddisk used 30GB with 'other'. With time the capacity just keeps shrinking. If I just stare at the screen, I just see the available space drop and drop. Until it hits Zero Bytes at capacity. 

Does anyone know what I can do about this? I cannot seem to find anything on this on Google. 

The only thing it returns on my keywords are things like how to remove temporary files, re-index size with Spotlight, Startup in safe mode. None of these things seem to work.



@Edit 22:02 06-04-2016

I have checked Activity Monitor and got the following results:


I have sorted on Bytes Written, that does not seem very strange.

However if I check the Graph Data Written below it gives:


As you can see the data Written is around 8.33 GB and a few minutes later already 10 GB,.. I checked; 'sudo fs_usage -f filesys' this keeps trying to get some attribute lists from mdworker? Don't know if that is normal?



@Edit 20:30 07-04-2016
With 'sudo fs_usage -f filesys' I see that the following processes write;


nsurlsession
nsurlstorage
IMRemoteUrlC
cfprefsd


With using Daisy Disk App I see the following:


So the private and library grows a bit, however the Core grows massively. I see that it produces a 'core dump' of around 528 mb every now and then. This tells cores is a folder for a core dump;

OS X El-Capitan - /cores directory taking up a lot of space?

What/why is this happening? (Like the post I have set the core dump limit to 0 and it seems to have stopped generating.)



PS: This is not a duplicate of Over 25 gb of Space Disappeared, I do not have time machine / Backups turned on.
Ah, these are core dumps. You can find more information on why they happen and how to prevent them here. In a nutshell, they are generated for debugging, but shouldn't be kept on disk by default. Either the system setting is wrong, or some buggy process is choosing to save them. Running 

sudo launchctl limit core 0 unlimited


in Terminal will disable the system from saving them by default, but still allow processes to make them if they choose to, or running 

sudo launchctl limit core 0 0


will disable them entirely, both in the system by default, and by disallowing processes from creating them. There should be no issue if you disable them completely.