I just got an answer back from Christina, 'the' professor on the German Axolotl forum. they will not harm your frogs, they are the creatures mentioned in my first post, if you change the water or put an air stone in they will disappear. this little bugger do not like clean water but they like your frogs excretions.
Google translation (very poor):
Swamp worm, Spirostomum teres
The swamp worm, length up to 400 microns, is rarely encountered in the plankton of a nutrient-poor waters. It feeds on bacteria and therefore loves eutrophic waters, where he liked staying in the mud.
In Spirostomum it is not, as the name suggests falsely to worms, but relatively large ciliates, Ciliata., The entire body is covered with eyelashes that are visible on this recording quite well.
Tip: The water from flower vases you can discover one of the three types of Spirostomum often after a few days.
OT question, what are the plants you have in the tank with your old, half blind Axolotl ? (YouTube vid)