Recently I removed all ad units except for one, in the hopes that the increased competition would increase the cpc. The following day I had delusions of reaping in tons of money as I saw my cpc climb to over $1.00 per click. Over the course of the next couple days the cpc dropped back down to slightly above what was normal for that ad unit. Now, the cpc did hold higher than it was when I had two ad units per page, but the overall earnings weren't really anymore because I was no longer getting clicks off the second ad unit.
Two nights ago I put the second ad unit back on the website, but made sure it was a completely different unit, and it's own channel. The cpc of the first ad unit on the site plummeted back down to about $0.20 cpc again, but the second ad unit is getting $1.10 cpc now! What the heck is going on? The ctr is much higher on the first unit than the second, so obviously I want the higher cpc to be on that unit. How in the heck do I gain some stability in my cpc? Is it possible to somehow switch the cpc from the second ad unit to the first? In the past I've tried just swapping the placement of the two units, but the cpc usually adjusts itself within hours.
BTW, this is a well established, aged site with pr3, and all original content. I haven't added anything new, or changed anything other than my ad layout in quite some time.