Frogspawn turning green and frothy

I have frogspawn from my grandads pond, their in the water they came in and its been 1week. Their tails are out of the eggs and some have 'hatched' but sunk. The water is turning green and frothy and I have read I need to change the water but they can not have tap water. Could I use river water as i live next one? Id like to do what I can to help them. Thankyou very much!