Black Moor suddenly not swimming

Question
Hi
I have a small black moor, Mahatma, which used to be the most active fish in the tank.  Always had a strange swimming action going up and down like a helicopter in a spin.  For the last two days it doesn't want to move and is resting near a rock.  Will eat a little if I place something right near him.

Looked at him very closely and physically he looks fine.

I have a 100 gallon tank containing about 10 fancy goldfish of varying sizes, some swordtails, rainbows and tetras.  Do a water change every week of 20%, feed a variety of fresh and dried foods.  Tank conditions test perfect.  The other fish are very perky and happy.

Really worried about Mahatma though.

Another question: Aquarium shop advised that the rainbows, swordtails and tetras get on with goldfish.  These smaller ones are a recent addition.  Is this information correct.

Thank you so much fo your help.
Kind regards
Mattie


Answer
That is normal behavior for a goldfish from what I have heard and seen.

If talking about Rainbows you mean 'Neon Rainbows' I'm not so sure with that. I heard they can be aggressive.  Sword tails and tetras should get along as long as you have a filter and a heater. The ammonia levels goldfish put out could harm the other fish but as long as you have a good filtration system you should be ok.