Stunted growth due to captivity?

Hello, I've been using the pond water method and I am aware that spotted salamanders lay their eggs around the same time. But I hatched salamander eggs about a month ago and the salamanders have barely grown. They have front legs and are starting to sprout back legs. I never thought that there would be anything wrong with them... till today. I was out collecting pond water and with a net, scooping up the extra daphnia swimming around and a caught a salamander larvae that could swallow my babies whole. Am I doing something wrong? Does captive keeping normally stunt growth? If I am doing something wrong would it be; a habitat not big enough, not enough food (they go through food in less than a day and the daphnia population always goes down at this time of year due to the excess larval pond life), or something else?
Thanks!
Gigi.

I found that Spotted salamanders grow very slowly to start with. Once they move off from Daphnia onto small chopped worm, they will pick up a little more. Make sure the water is clean , as in no ammonia etc and the food is plentiful at all times and all should be good.