What media do you have in the ACs? I had similar problem, till someone suggested I add a layer (or two) of batting: http://www.poly-fil.com/batting.asp
You can get it very cheap in walmart.
I had gotten it from the bedding/hand-crafting section at Walmart - I think I paid $4 or $5 for the poly-fil bag and have been using it for ~8-9 months now.
This is very fine material (I think it is used in pillows/bedding), and has *drastically* improved the look of my tank - the water became much clearer after I added it.