So I've been meaning to post for the last week about my experience with macropore, but life kept getting in the way! For anyone who comes across this thread in future, better late than never I figure.
Step 1: checked my test kit by testing RO water at the same time. As you can see, the test kit was reading fine but my tank nitrates were through the roof.
I added 375ml of macropore to my 440L tank last Sunday. I didn't have time to dismantle the filter (plus something always goes wrong and I end up dumping water all over the carpet), so I just hung it in my tank in front of the power head:
After 24 hours, I did the first test. Nitrates were way down to 10-20 already.
After 48 hours there wasn't a huge amount of difference, but it was closer to 10 than 20.
After 48 hours I got bored of testing my nitrates every 24 hours. Jeez, do I hate that test kit. </rant> Ahem. So after 1 week, I managed to get the macropore into the filter (without too many accidents) and the results are great - looks like 10 to me :)
Can't say that the shrimp look that much different yet - I don't know how they survived so long with such high nitrates (and don't get me started on the Ph), but for now it appears to be stable.
Thanks everyone for the input!