The judge is permitted to ask a question of a witness even though he is supposed to be the judge, not an advocate for either the plaintiff or the defendant. However, the judge should have permitted you to further cross-examine this witness or follow up on the answers the witness gave to the judge's questions. Of course you could raise this issue during your appeal, although it seems unlikely this would change the outcome of the case. ( based on the limited information you have provided)
It would not have been proper for you to make an argumentative statement (such as "the witness is not credible") during your questioning. Such an argument would be proper during closing argument, not during cross examination.
You could have objected to the judge asking a question, but you would be unlikely to get a positive response since the judge would be the person to rule on your objection and the judge was interested in the answer. Further, the witness (or his attorney) would be entitled to elicit an explanation during redirect even if the judge had not asked a question. Because of this, the circumstances you outline are not likely to give you grounds for a successful appeal.
Courtroom procedure and the rules of evidence are not easy topics to fully absorb. This puts you at a disadvantage when you are acting as your own attorney.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.