Afrrican cichlids

Question
QUESTION: Hi Lynda,

I have a 75 gallon tank that I sat up two months ago. My fish have been fine until last week when they started dying one by one. I only had six and I m down to three. I do about a 10% water change every couple of weeks and my levels have been fine. I took a water sample to the fish store where I bought them after they started dying and they said my water is fine.All levels were fine. However he did not test for chlorine. I do use tap water but added the chemicals for safely adding it. It seems like there have been an explosion of algea as well. Can you help me?

ANSWER: Hi Kelle,
Algae will not kill fish, and most African Cichlids do eat algae.  If all your water levels were fine, and all your fish died, I am at a loss to know what happened.  Did they check the ammonia, nitrite, nitrate, and PH level?   Does your tank have enough oxyen?  Your filter should splash water back into your tank causing water movement.  Adding air stones will help.  Do you have a killer in your tank?  I ask because some fish will kill tankmates.  Not knowing exactly what fish you kept, I really don't know what could have happened.  Water changes should be 25% every week to keep fish healthy.  10% water changes is not enough.  Adding a good water conditioner ensures you that the water will be safe.  Did you have a drop in temperature, or maybe your thermostat is broken, and brought the temperature up to quickly.  Temperature that drops, or goes high quickly will kill fish.  
I'm sorry, this is all I can think of.  Keeping African Cichlids is lots of observation.
Lynda

---------- FOLLOW-UP ----------

QUESTION: Lynda, thanks for getting back to me. I have a good filter system and also some air stone no drop in temp its always a consent 78 degree's d they checked all the ph, nitrite and nitrate levels s well. I can't figure it out but im sad I am losing fish. I may have a killer though I hope not but I have one that is pretty agressive with the others . Any thoughts?

Answer
Hi Kelle,
This is a mystery to me.  It may be that you had a virus, some kind of bad bacteria in your tank.  Do water changes of 25% every week, this is so important...apart from this, I really have no idea what happened in your tank.  I'm sorry, I cannot help you more.  Do not feel bad, whatever happened is not your fault.  I have heard of this happening before, fish dying one, by one, with no apparent reason.  Mystery Deaths.  I'm wondering about your fish though.  Could you tell me the names of the fish that are still alive in your tank?
Lynda