Did the normal tank check including my son's tanks and noticed one of the
mollies was not swimming around as normal....Son checked in depth and found
her at the bottom of the tank curved round herself.

We did a quick water check - ammonia was 0.1, nitrites 0 and pH had risen to
8.5 - normal is 7.5

I caught her and bagged her while deciding what to do....she was physically
sick....

At the moment, with little other option, I have done a 30% water change and
put her into a breeder trap...

I will do another large water change tomorrow to get the ammonia down and
the pH starting up to normal levels. I'm also going to add another
pump/filter with mature filter medium.

The other fish all seem to be very happy. No new fish added for 2 months
plus. 15gall tank with 3 Mollies and 4 Rosy Barbs.

Has anyone got further suggestions (other than monitoring more closely the
water changes done by my son - who is very remourseful)

Gill