Real interesting thread this!!
I was just reviewing one of Jason's (aka squidviscious) reports here and stumbled upon this.
Apparently 'Instant Ocean' seawater lacked the element Strontium; in the absence of which proper development of the statolith in cephalopods was prevented. The squid were referred to as 'spinning cephalopods', as balance in the water column was not possible, and they were unable to capture food, in addition to having abnormal embryo development (Hanlon 1990).
Now I'm not familiar with these artificial salts, and 1990 was a few years ago and the problem may well have been remedied by now, but if anyone has a packet of this 'Instant Ocean' I'd be quite interested in finding out whether Strontium is identified as one of the trace elements.
Jason's ref is (so I hope he has these details correct!!):
Hanlon, R.T. 1990. Maintenance, rearing and culture of teuthoid and sepioid squids. Pp 35-62 in 'Squid as experimental animals'. Gilbert, D.L.; Adelman, W.J.; Arnold, J. (Eds). New York, Plenum Press.