Just an update...
I swopped out the filters in two of my 10g tanks. This seems to have helped significantly. The nitrite in the "good" tank went up a little as a result, to about .20 ppm, so i did a water change and retested a few hours later to find it at 0ppm again.
The second tank which received the "good" filter cartridge" has finally regulated as well (for the time being), and i also did a water change and retested a few hours later to find all readings (NO2 and NH3/NH4) at 0ppm.
As far as the smaller tank, still remains at 0ppm for both items.
The larger tank is another issue. I am going to continue with 20% water changes daily. Is this too much or too little for a 30 gallon? I gathered some gravelw/bacteria into a stocking as suggested and have been suspending it. I haven't done a test yet, but am about to do it.hopefully things will look a little better although i don't expect as dramatic a change in the larger tank. My guess it is easier to "cycle" repair a smaller tank with fewer inhabitants.
Thanks for everyone's info...and if you have further suggestions they are appreciated.
-cb