squid, has internal gearing that alternate the flow from left to right every 30 seconds i believe. huge (and i mean huge) thread on that particular item over at --. also just do a search for "squid wavemaker" on a search engine and you should get a ton of hits.
this has nothing to do with the wavemaker...i was just curious, how do you like your brittle star? i just got one and he's kinda freakin' me out.... what about you?