sitting at bottom

Mel wrote:

One of my fantails (4 years old) has been periodically sitting on the
bottom of the tank for the last few days. He swims about every so
often, then returns to the same corner of the tank and sits there for
a while before going off for another swim again. He has also been
yawning frequently. He is eating as usual and has no other symptoms.
My water parameters are fine (ammonia 0, nitrites 0 and nitrates 10,
PH same as usual) and I haven't introduced any new fish for at least 2
months. Has anybody got any idea as to what could be the problem? It's
quite distressing to see him sat there looking so miserable and I
desperately want to get him back to his usual self.
Mel.

Is the temp warmer than usual?

Anyhow, it can't hurt to go with a 50% water change with treated,
temperature matched water. See if that perks him up...

Others may have additional advice...

-D
--
"There is nothing so strong as gentleness, and there is nothing so
gentle as real strength." St. Francis de Sales