Rock candy is what i use for slow release of sugar the clear kind to not color the water JOKE. I can see how this can be usufull but in a glass of water with sugar you are making sugar water which is thick especailly with all the sugar disolved. So in that case i would also expect things to die seeing how they have to absorb what they need. So pretty much what you did is poured syrp into a glass
. But i expect in a 50 gallon tank 1 teaspon evfery 2 to 3 days would do nothing but get used up by the bacteria that multipies like rabbits in you tank
Just my 2 cents