lyretail molly acting strange

Question
Hello Ron,

I have a 20 gallon tank with 15 lyretail molly and 1 Pleco - Suckermouth catfish. Things have been generally good for the last 6-7 months. I have been doing regular water changes (every 3 weeks) and filter cartridge changes (every 2 weeks).

Since 3-4 days, one of my lyretail molly has been acting and swimming strange. It stays vertical and keeps swimming in circles staying vertical. I immediately did a water change, filter cartridge change and added some mardel anti-bacteria medication. I did not see any change in the behavior after a day. I tested for nitrate, etc and all looks good. Also today morning I saw one more molly showing the same behavior and the other one still behaving same along with signs of loosing balance.

Not sure if my description is clear. Thanks in advance for the help.

Regards,
Darshan

Answer
Hi Darshan,
  It is hard to say exactly what is wrong; however, I strongly encourage you to do more frequent water changes; once every 3 weeks is not really enough.  I strongly encourage people to change 25% of the water once a week, every week to keep their fish happy and healthy.
Many times, simply providing good clean water is the best remedy because it allows the fish to deal with whatever ails them.  Poor water stresses a fish and makes it much more susceptible to any external problem.

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>