Shellies for each fish, not shells per gallon.
http://www.cichlid-forum.com/articles/l_ocellatus.php
In the tank, these cichlids should be supplied with at least one shell each. If you don't have access to
Neothauma shells, escargot shells from a grocery store or delicatessen can be used as substitutes. Exercise care in selecting shells; don't use shells that are likely to "trap" a fish in its spirals. Each shell-dweller needs at least one shell because they use them for shelter from predators and as a site for egg laying and brood tending by the female. Even though you may not have any other fish in the tank, they will still hang out near and even cling to their shells. In other words, they are necessary to give these tiny fish a sense of comfort and well-being at a minimum.
If you don't provide enough shells, one of your fishes will get beat up and you'll probably find him ostracized to the upper corners of the tank. It's important to have at least one extra shell (if not more) so that the
ocellatus have some choice among the shells. Furthermore, their young will need a shell once they get evicted from their mother's.
Males need an area of floor space with a 6-inch radius, which they guard vigilantly. This is not a ferocious cichlid, but neither is it afraid to attack intruders many times larger than itself. About two months after my first colony was established in their tank, I decided I'd add a few more shells. One dropped right in the center of the male's territory. He'd already claimed four shells and so I thought a fifth one was out of order and proceeded to put my hand in to move it. No sooner had my hand gotten within 5 inches of the shell before the male had bitten my knuckle. Needless to say, I ended up moving the shell with something other than my hand!
ocellatus have even been known to attack Python siphons
