I have just removed one of my powerheads from my 250 litre as it was turning the tank into a washing machine, Newave 2700, a tad too strong maybe? it'sonly 2 mths old and is up for sale, I still have the 1600 in the tank which is adjustable for flow rate and seems spot on imo, 2000 could be ok Martin but if your planning on keeping them where your 900's are at the moment facing the front of the tank they may be a little strong for you, I wish I had 2 of my Newave 1600's as they have a sleeve to adjust from 800 to 1600 lp/h and aren't any more intrusive than your nano's, they're well made too and a couple of quid cheaper than the K's. Got mine from uncle Rich at AE 😉