There is also a big factor to remember as well with the flow meters from GHL - they also have an internal dimension and you don't want this smaller than your own pipe (irrelevant of flow specifications) as if your restricting the flow going through the meter this will only add to your issues... I use a 9000 to measure my 500 litre requirements at its the same size internal dimensions as my pipe.
I was running 2x 12000 Jeabo and couldn't work out why my flow was restricting even after redesigning my 32mm pipe for max efficiency it was the flow sensor causing all the issues (I wish here GHL would add just one more sensor for bigger tank users with 32mm connection )
I recently had to change my tank to a smaller red sea reefer 525 and I have my flow sensors on my return line, I've used my vectra l1 and it would only show 3.5K at 100%, I knew with pipe restrictions 25mm instead of 32 I would loose head pressure but there was a pre fabricated part the significantly reduced the flow back into the tank casing the issue, so I redesigned this so I can acquire the turnover I wanted within the tank.
Restricted area below - red sea what you thinking

look at the 90% reduction wtf
Attachment 8452
Bookmarks