so i remember someone mentioning oxygen levels deplete during the night since plants emit o2 during the day and emit co2 during the night. either way...the key thing i remember is that night = lower oxygen.

so my black moore, Blackie, has been gulping at the top of the water for awhile now. but only at night. during the day, he's completely happy. but once it hits 10pm or so, he starts gulping at the top for air. he's by himself in a 20gal, water params are good. the pH of the water is on the lower side around 7 - 7.3, water out of the tap is 6.5. 20 nitrates. 0 nitrites. i have 2 plants in the tank. a penguin 150 biowheel filter along w/ a bubble wand. i used to have a bubbler in the corner, but ever since he started gasping, i changed to a bubble wand, hoping to increase oxygen levels. but it seems no improvement.

why's he still gasping? do i have to get rid of the plants? are they depleting too much oxygen during the night?

I don't think 2 plants would deplete the O2 that much.

From my experience with my fish, I found that some fish are just "air-gulpers", maybe cos they like gulping air. I got 5 fish in my 55 gal tank, 4 almost never come up for air (they only do so during feeding), 1 fish (which is my biggest fish) likes to hang out at the top and gulp air for long periods of time. They are all healthy and happy, so I don't think it's a problem.

Do you already keep the bubble wand on at night? Whatever's going on, extra aeration will at least keep him comfortable. Does he have any trouble chewing or eating? Any other strangeness?

no other strange activity. he's kept to his routine of begging for food when i'm in front of the tank, floating on the left side of the tank to stare at me while i'm using the computer, or minding his own business when i'm at work (so i would assume).
i leave the bubble wand on all day. and he's a bulldozer during feeding time.