Flattening Low Grit Synthetics

How do people flatten low grit stones? I have a Naniwa 220 pink brick that I have used to thin a few knives now and it has dished quite a bit. I have an atoma 140 but the low grit stones really seem to wear away at the diamond plate over time. Is there a better way?

I think part of that just comes with the territory with it being so low grit. There's flattening powder that can be purchased in pretty low grits (I think I've seen like 60 or 80 grit before even) and you just shake a little out onto a flat glass or ceramic tile or something with some water and put the dished face of the stone on there and start moving it around, varying your motions, champfer the edges and corners, etc.
http://www.ebay.com/itm/252336203621?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
Slow but it saves your diamond plate some usage
I swear my 220 pink brick sucked some of this abrasive powder into its porous surface...

Why not do the majority of the work on concrete, tile, or something else that's cheap, but fairy flat, then when you're flat using the cheap method switch and finish up with a diamond plate?

Belt sander and then the atoma.

My old DMT for the 220. Atoma for the higher grit stones.

Lars

Wait until you have another low grit stone that needs flattening, or another medium grit stone that REALLY needs flattening....

Thanks for the advice everyone, I'll give it a shot. I have a cinder block that I'll try for now. The swarf coming off of it seemed to be more concrete than pink, but maybe I just need some more elbow grease into it. I didn't know about the powders, thanks for the tip.

I use a cheap 140 grit diamond plate that I got from a site that I'll not mention here. As I use it only for flattening it does not seem to wear out quickly. I have two years of use on mine at the moment. However, I don't often use stones below 500 grit, as such I do not have to flatten them often.

I've found i flatten less and less the better i get at using the whole stone. I use a diamond plate mostly to clean off a stone clogged with metal.