for starters he's a *censored* for selling you that and you can just hook a clean one up to the hole-hole and tape them together
Mold is a common occurrence in ant-keeping. Mold is usually uncontrollable, and often quite harmless in test tubes to an extent. Ants live in similar non-sterile conditions naturally, and having your test tube a bit dark won't harm them - but needless to say a fresh tube is always good. Regarding his case with the water, it goes along with the mold/age of your tube. While the seller should have provided a fresher tube, I don't think they were necessarily a terrible person for providing a tube that needed to be changed.
OP, you can simply take another tube and hold them together then tap the colony into the fresh one. Light taps on a hard surface will not cause significant stress to a colony and is in my opinion the most efficient way to move a colony out of a tube. You could also tape two together and cover the new one up so they move to the darker area.
Edited by Kevin, January 28 2018 - 3:41 PM.