Apps (activities) are usually cached, and "use" RAM. When RAM is needed, though, cached apps are "killed" to make space. This is all handled by the LMK (you can Google it if you want more information,) automatically. So in a certain aspect, free RAM is wasted RAM - if it is needed, it'll be made available. Struggling to get more free RAM is useless.
Take killers are also bad... Not only do they go against what I described above, but some apps use services. Those run in the background to provide various utility to the app, and can restart when killed. Task killers will kill them, but they'll only restart. So you'll only be gaining more CPU usage, more battery draining, and your task killer will actually be using RAM for itself.
In short: it'd probably be best if you got rid of your task killer, and learned to stop worrying (about the RAM) and love the bomb.