Hi lb, I don't think I have welcomed you to
HCRU yet, so I'd like to say hello and thank you for joining our crabby family
This is an excellent question, btw. There are definitely "conditions" to my ISO'ing new crabs. In general, I strongly advocate ISO'ing all new crabs for at least 3-4 weeks before adding them to your established colony in the main tank. The reason is because
if any of the new crabs are carrying pathogens it is possible the sickness could quickly spread to your healthy crabs (especially if any have a weakend immune system or are vulneralbe because of an impending molt). It may take a few weeks for the sickness to spread-much like the incubation period for illnesses in humans-it takes a while for symptoms to start rearing their ugly heads.
Now, if I go to pet store A (with fairly decent conditions) and purchase some crabs and then go back a few days later and purchase a few more from the same shipment, they would all go into the same ISO tank. If a few days later I go to pet store B and purchase crabs, I would most likely put them in the same ISO, unlesss pet store B's conditions were absolutely horrible-ie; dead crabs and limbs all over the place, then I would consider a seperate ISO. Also, and I know this sounds horrible, I consider the quantity too. If I purchased 10 crabs at pet store A, I would not put the new crabs from pet store B in with them-because it is pretty expensive to chance losing 10 crabs. But if I only purchase 2-4, I would weigh the odd and most likely put the crabs from pet store B in the same ISO. Hope that made sense LOL without sounding too crude.
In addition, if any of the crabs have mites, that crab or group gets bathed and goes in their own ISO-other than that, I do not bathe my crabs at all. Not newbies, not post molters, etc... I have not done so for 6 months and they have been doing wonderfully. I do provide deep enough dishes for them to self bathe if necessary and I have recently purchased a nice, small, personal humidifier that emits an ultra fine mist that I use in the tank. The crabs, especially my straws, flock to the "foggy" area when I turn it on so I have deduced that they enjoy it