Nope. They only catch ich if there is an infected fish amongst them.
Erratic swimming patterns for your cardinal tetra can be attributed to several conditions. If it is unable to balance itself in the water, then it might have swim bladder disease.
As for the guppies, at times they will just hang right beneath the water's surface. This is usually the case if there is insufficient aeration, but sometimes they are just skimming the surface scum. You need not worry unless they are exhibiting signs of stress and disease.
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