I purchased a male sailfin molly not too long ago and pretty much right away I noticed he spends most of his day just gasping at the surface. He's in a 20 gal with 3 females and I do a 50% WC once a week. Tank's been running for 5 years and has proper filtration and aeration and is at 78 degrees. I know my tap water is high in nitrates.. always has been straight outta the tap. Could that be the problem? I don't see any spots or fungus or anything on him. He's so nice lookin'.. so I'm hoping he gets better and gets to breeding with my females. And ideas on what could be wrong and how I can fix it?