My regal tang either suffered some kind of eye injury or has pop-eye

. Ive done two large water changes this week in hopes of bringing my nitrates down a little(15). It looked a couple days ago like the swelling in it had gone down but it since has ballooned up again to where it looks like it about to explode. He doesnt seem to be visually impaired atm, still eats like a pig and is acting normally. Im not sure what else to do about it.
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260g mixed reef, 105g sump, water blaster 7000 return, Bubble King SM 300 skimmer, Aqua Controller Jr, 4 radions, 3 Tunze 6055s,1 tunze 6065, 2 Vortech MP40s, Vortech MP20, Tunze ATO, GHL SA2 doser, 2 TLF reactors (1 carbon, 1 rowa).
http://www.canreef.com/vbulletin/showthread.php?t=50034 . Tank Video here
http://www.vimeo.com/2304609 and here
http://www.vimeo.com/16591694