Anglefish Dying

Question
QUESTION: I have a 55 gallon fish tank that has been up and running for about 4 months now.  I have a bio wheel filter, the temp is kept at about 78-79.  I have tested the water (PH, Amon, Nitrite, Nitrate, softness) and everything comes up correct. I have 4 mollies, a pleco, and 4 neon tetras.  I bought 4 small angles(body is about the size of a quarter).  One died within 2 weeks.  One just died this weekend.  It has been 4 weeks since I put them in the tank.  I feed a tropical flake with Bloodworms and baby brine shrimp. I do have some live plants, Water Sprite and Wisteria.  What could I be doing wrong? I don't want the other 2 to die?  I do water changes about every 3 weeks and the filter every 4 weeks.

ANSWER: Hi Jenni,
How high is your PH?  Mollies, cannot be put in with Angel Fish and neons.  Mollies need hard alkaline water, and Angel Fish, and neons need acidic soft water.  25% of your water should be changed every week.  The sponge in your filter should not be changed once a month as it is full of good bacteria.  A sponge lasts a long long time.  You rinse it in the same water temperature as your tank water, as to not kill the good bacteria, and it should last you for well over a year.  The carbon should be changed monthly.
Since your water chemistry is correct, something is wrong, and it could be the PH.  Your PH should be between 6.5 and 7.0 for the Angel Fish...  and 7.5-8.0 for the Mollies.  If your Angel fish were kept in a tank with a low PH, and you PH is high, this is what could be killing them.
I don't know what else it could be seeing as your water chemistry is correct, and no other symptoms appear on the angel fish.
Hope this helps
Lynda



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

QUESTION: My PH is 6.8.  My mollies seem to be doing fine.  I don't have a sponge in my filter.  I have a bio wheel - hang off the back Marineland filter.  I'm changing the carbon cartrige that has blue screen on the back side.  The directions on the filter say to change it every 4-6 weeks.

Answer
Hi,
This is a very low PH for Mollies, and one day something will show.  They need alkaline water, and salt in their water in order to live healthy lives.  
The Angel fish should be doing well, I can't think of anything else that could be wrong.  It is hard for me say what they are dying of, as I have nothing to go on.  There water is perfect, they have no fungus, ick, or anything apparent on their bodies.  Water changes should be made every week, as once every three weeks is not enough.
I really don't know what caused the death of the two angels, I'm sorry, but cannot help you more.  Sometimes fish die and to find the cause we must dissect the fish as there are so many diseases.  It had to be internal.  Do you know if these fish came from a breeder, or directly from a lake?  Sometimes fish do not take well to a change, and maybe the ones who died were weaker than the two you have now.
I hope that they will survive.
Lynda