Earth Eaters Part 2

Dead spaces are pockets whereby water do not move, hence, they are areas whereby poisonous gases can accumulate. Usually they are in corners, under driftwood, etc...on the bottom level of the tank. Because EEs go down to the bottom to sift, they are more susceptible to being poisoned.
To eliminate the deadspaces, one needs a gentle current, this can be from the filter output, a wavemaker, or even an active UGF. Anything that moves the water at the bottom and not let it remain still for a long period of time.
I think plecos and catfishes will have the same problem, ie sudden unexplained deaths arising from dead spaces. As these fishes are bottom dwellers and like to hide beneath driftwood and so on.

The other aspect, which I have omitted is the oxygen level in the tank, it is something which is often neglected much to the fish's detriment. Surface agiation, air stones, all help to raise the levels. In a packed environment, oxygen availability becomes even more important.