jess wrote:
Advice from LFS that he is probably under a year according to size. I
did a 20% change on the 11th using a conditioner and readings today
were nitrate 10 mg/l, nitrite 1mg/l, gh 6, kh 3, ph 6.8. Tank is 6 UK
gallons and has a fluval plus 1 filter, gravel, a few larger pebbles
and some live plants. There is only the two comets in there and the
other one is his normal self. I know they will need a larger tank when
they grow but thought this would be ok for the next few months tillI I
move house. Since this afternoon he has mainly stayed at the bottom
and only occasionally swimming around although he is still eating and
has pooped. Even when moving his dorsal, pelvic and anal fins remain
close to his body so it is all very worrying.

From the figures that you give it certainly sounds as if the tank is
cycling - the symptoms that you are describing could well be nitrite
poisoning (clamped fins). It would be helpful if you could get the
ammonia reading for the tank as this would indicate what stage you are
at in the nitrogen cycle - it could be that the cycle is advanced as you
are now getting nitrate readings but this information would be valuable
in suggesting the next course of action. You are looking for 0
ammonia/nitrite and a positive reading on nitrates. Your pH is
relatively low which is good - ammonia is more toxic with higher pH's.
You could try adding some aquarium salt into the tank - this will
eleviate any nitrite poisoning (not cure) and make your fish more
comfortable - I've used 1/2 the recommended salt solution before to
treat parasites with no ill effect (but this was with tropicals). Cut
back on your feeding all the time that you are getting positive nitrite
or ammonia readings - try fasting them for a day and then feeding a
small amount daily (or even every other day) until the tank is cycled -
you can then gradually increase it - however hungry the fish make you
think that they are they will not suffer

If possible try and get some used filter medium or gravel from a friend
or your LFS - this will have the effect of "seeding" your tank and
speeding up the cycle.

Good luck
Gill