Thats your flow restrictor.
Ive got a 450 from collins, left it to run a few hours and it worked fine after that...
What seems odd is your waste/pure ratio, also i would personally think your tds should be lower....
Have you given lee a ring?(from collins) hes a pretty helpful guy...
Edit : if you havent got it sorted later i'll take a few photos of how mines plumbed.
Although its simple enough as they're in parallel