If you post a picture I'd be happy to try and identify your specimen. Are you thinking it might be tiger salamander larvae? If so, it can sometimes be difficult to tell them apart based solely on appearance. The best way to tell them apart is your source. Since axolotls are captive bred, they are likely to be sold small, and likely to include color variants. Tiger salamander larvae are often sold at larger size and will all be grayish/brownish.