1 Fish going crazy rest are fine need urgent help

Hey all,



First of all thank you all for the informative posts here ! I have learnt so much!



I have a problem with my Coral Beauty fish which after my most recent water change, ( 80Litre Tanks Changed 20Litres weekly) has begun swimming up and down the front of the glass all day very fast, and occasionally darting around the tank stirring up the sand bed ( this only happened today ) It usually eats well at feeding time but since the water change only has a little bit to eat.



Tank Size - 80Litres

Ph- 7.9-8.0

Salinity 1.024

Ammonia - 0

Nitrate - 0.80 ( why so high ????? First time ever ! how to reduce ?? )

Nitrite - 0.5ppm

Water temp - 26-27.3 degree celsius ( Im from Australia so its bloody hot but the hottest is around 27.3 degrees Celsius )

Fish -

1 Small Clown male

1 X Mandarin Fish Male

1 X Mandarin Fish female

1 X Magenta Dottyback

2 Hermit Crabs

4 Turbo snails small



Coral



1 X Sun Coral

1 X Cataphylia

1 X hammer





All the other fish and inhabitants are fine, living and eating well, its only my coral beauty swimming up and down around the tank really fast likes shes stressed



She has no signs of ich, or fungal growth seems in good colour condition as well !



Any help would be greatly appreciated !!