Gold Fish keep on dying

Question
i have an almost 300l fish tank which i keep about 20 gold fish, however i changed the water after 2 weeks.suddenly the water turned greenish,i kept on changing the water on 2 day intervals.Now the water is getting better but the fish starts dying one by one and they are not eating,not active.Please help.This is the third time happening.

Answer
Hi Godfrey,
 When you say you "changed the water", did you change all the water?  You should really only change 25% at a time, 50% maximum.  If you change more than that, you upset the balance of microorganisms in the water. That could cause the symptoms you observed.  

-- Ron C.
  rcoleman@cichlidresearch.com
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