hey im in desperate need of help i cleaned my fish tank out 2 days ago as i normaly do with about 20% water change but all of a sudden i tested the nitrate and it was really high and i dont know why its never happened before iv had my tank for about a year now and everything has been fine just a bit worried that im going to loose all my fish as iv had 3 die in the last 2 days one gourmis and two white cloud minnow and iv recently had 4 platty fry and was so pleased that i managed to breed and really dont want them to die what shall i do???