if you got them 3 weeks ago-how have you been keeping them since, and have you fed them anything? not to be too blunt here, but this info is needed before you get some-or within the same day since they are aquatic animals - and water quality is very important to their basic health (bad water=death), there is a section of the caudata culture part of this web site will all the data.
you need to explain what you have been keeping them in since, how you have been keeping the water, if they are eating anything, are they loosing weight/being lethargic, are they eating each other (which will happen even with food available)..describe them (how old, what size)..etc