high nitrates...anyway, u should perform surgery..if left like that, the gills will be exposed to bacterial infection which in will eventually kill the fish.
yes gill curl is commonly caused by bad water and/or diet, however surgery should be your last option!!!
As long as its not too severe, just install a powerhead.. Give the aro some current to swim against as well as making sure the water quality is good of course.
I have saved quite a few aro's from surgery with just a powerhead.
if the curl has just began kepping water in tip top condition would reverse it. but if it already has this condition for a long time, surgery is required.
I should have read more. a 12" aro has plenty of turning space in a 150, but not for long.. if there are to many decorations in the tank this could be a possibility though.