Hi. Sorry to hear about the problem your Parrot Fish is having and also please forgive the delay in responding to your question as it appears it was originally posted to another category and just arrived here in the Pet's Category.
Your fish is suffering from a disorder called Swim Bladder Disorder (sbd). The swim bladder is an organ fish have which enables a fish to swim upright and maintain its buoyancy. When it becomes full of air, infected or blocked it ceases to function correctly. The shape and anatomy of Parrot Fish make them highly suceptible to sbd.
The best way to treat this is by beginning with a 25% partial water change.
After the partial water change begin to feed the fish canned peas without the husk as the peas should help clear out the fish's swim bladder which has become compromised as a result of the sbd. Feed 1 pea twice a day. You can also try fasting the fish for one day, feeding the peas the next day and continue doing as such for 10 days=one day feed--one day fast as this will sometimes fix the problem.
In addition to the above it would be helpful to add an anti-bacterial medicine to the water as some cases of sbd are caused by bacteria in the swim bladder. A medicine such as Maracyn-Two is a good choice to use in this type of circumstance. Click on link below for a view of the product.
Keep in mind that it's important to maintain excellent water conditions which can be obtained by doing weekly 25% partial water changes and to not overfeed the fish.
Please note that Parrot Fish, although a beautiful and unique fish, are not very hardy mainly because of their shape and the fact that they're a man made breed which occured through breeding two different types of cichlids, Parrot Fish are also known to be sterile but who knows--this could change.
In addition to the link re: Maracyn-Two, listed below is another link. This link will give you some additional information re: sbd.
Best wishes and please let me know if you have any questions.
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=4842
http://badmanstropicalfish.com/forum/index.php?topic=1026.0
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YOUR TROPICAL FISH RESOURCE
OVER 20 YEARS EXPERIENCE W/TROPICAL FISH---BREEDING, MAINTAINING, CURING
You're most welcome.
Canned peas can be used to feed the fish or parboiled frozen peas both without the husk.
It would be preferable to put the fish in a seperate hospital tank.