Here ya go. Feedback from Tetratec: -
"Thank you for your email,
You are correct that the max flow rate of these canister filters is calculated without filter media in, at a lift of 1 metre. It is important that the flow rate is gauged in standard conditions, introduction of filter media would then introduce further variable that would add ambiguity.
The actual flow rate depends on the condition of the media, the length of the pipework and degree of clogging, the degree of bends/ kinks in the pipes, the lift, the condition of the impellor and many other variables. Under very unfavourable circumstances the flow rate would drop further than ½ the quoted figure. However, in new filter, with clean media and pipes, I would predict a flow rate of roughly 900-1000 lph."
So, if I'm hot on filter maintenance with 2 tetra tec ex1200 running at say 1800 lph that's the tank turned over 6 times. For an overstocked mbuna tank, that is not great. *sigh* Wish I had room in the cabinet for that FX5! I'd have had two of 'em running together. I'm sure then ther would be a whirlpool in the tank! *grins* ... but at least it'd be clean.
L