Sitting on bottom of tank

[guppy grandma]

One of my orandas has started sitting at the bottom of the tank and only shows interest when food is about, then he whizzes about normally. When the food is gone he's back to the bottom of the tank again. Looks perfectly fine, no spots etc. Any ideas please?
ammonia 0
nitrites 0
nitrate 40
PH 7.6

90 litre(euro) tank 3 orandas

 

[bruinsbro1997]

Nitrates seem a little high, a PWC would bring it down a bit.

On the other hand...

That's about twenty gallons which is only good for one goldfish.

 

[guppy grandma]

Thanks for response, I keep forgetting to do UK/US conversion, its about 24 us gallons. I did a large water change yesterday and the API info on the nitrate leaflet says 40 or below is ok. But, if you recommend it should be lower, I will happily do another pcw