Leeks seem to respond to a liquid feed much easier than feeds. We put it down to the fact that when it's applied, much of it gets caught up in the folds at the top, and while you might think this discolours the veg, it doesn't appear to, and the stuff can easily get down to the roots at some stage later!
We use 6x tea, with any comfrey/nettle tea we have, and they love this mixture!
Our days of growing around 250 leeks down on 'The Patch' are over now, so 40 or so at home are enough for us!