[canadawest]

I've had a pink/black hawaiian cuke and two tiger-tail cukes in my tank for almost two years now. The Pink cuke is active day or night, while the tiger-tails are only seen at night.

I'd have to say each species works equally hard cleaning up the sand. I wouldn't hesitate to recommend either as a good sand cleaning critter. I would also recommend including Nassarius snails and fighting conch (Paul's Aquarium had some in on Fri) to your sand critter list as they both do a great job stirring up the sand and cleaning it of detritus.

And yes, the darker "turd" looking cukes are all mostly harmless. I've never been concerned about mine poisining my tank, mostly because all of my powerheads and intakes have screens on them and the fact the tiger-tails are never on the glass, so no danger of climbing even near the powerheads. The hawaiian on the other hand likes hanging out on the glass, but has never yet come near enough to any of my 4 powerheads to cause me any concern.