Aquarium Care & Fish Loss

Question
QUESTION: Dear David,
My wife cares for a 75 gallon tank of freshwater fish.  There are fantail guppies and fry (many), also 3 sword tails (& fry) and 23 algae eaters and a cat fish.  The problem is that she has had a fair fish loss since getting the new tank.  We change the water and clean the rocks 1 X (every) 2 -3 weeks.
We just changed the coarse and fine filters in the Eheim filter.  She uses water treatment for the water and also some Cycle type product.  What do you think she is doing wrong?
Sincerely,
Howard Buchin

ANSWER: Hi Howard:  I would start with asking how many fish she has lost?  23 cat fish is about 19-20 too many for that tank.  What is the water chemistry of the tank?  What is she feeding the fish? How often is she feeding the fish? What do the fish look like as they are dying???  dave

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

QUESTION: Hi David,
In follow up to my question.  My wife has lost about 1 fish per week for the past 4 - 5 weeks. She has one cat fish (small) and 2 or 3 algae eaters.  She feeds the fish once per day.  Dying fish swim on their sides, near the bottom of tank.

Answer
I would feed the fish twice per day... no more then they can eat in 3 minutes of time. I would also supplement the bottom feeders with algae wafers.  Are the dying fish skinny? Fat? do they have any kind of white cotton looking stuff on them? does the illness just come on suddenly? are they female and males or just one gender?  She may need to do more frequent water changes... let me know... dave