Gasping goldfish

[OneTwoRedBlue]

I have two common/comet goldfish at my work (OneFish and TwoFish), and OneFish has been gasping regularly at the surface for a number of weeks. TwoFish is a little smaller and doesn't seem to be troubled by whatever is bothering OneFish.

The gulping is worst mid-morning and lessens towards late afternoon. She'll swim around a bit and then come up to the surface and gulp maybe 10 times, go down and poke gravel/plants before coming up again. Often she'll do it enough that she suffers buoyancy problems and floats unhappily at the top of the tank.

I tested ammonia, nitrite and nitrates today. 0ppm, 0ppm, ~20pmm respectively. The water temperature is 24 deg C. Didn't test pH today but it has always been around 7.4-7.6. Ammonia and nitrites are always zero, nitrates typically around 40ppm.

The tank is 150L (40g) and has been set up for almost nine months. It has a Aqua One CF1200 cannister, stated operating flow rate of 750L/h (~200g/h) with a spray bar a couple of cm above the surface of the water providing agitation.

The last water change was four days ago, I do them weekly and replace around 20% of the water.

We've had OneFish for about a year, she was initially in a bowl. TwoFish has been with us for at least six months.

Gasping behaviour has been consistent through addition/removal of decor, plants, two 90% water changes and one large clean.

I feed them Nutrafin Max Goldfish Color Enhancing Pellets (sinking), and occasionally give them peas. No changes to their diet.

Any ideas on what is wrong? I've ordered a cooling fan (link) to bring the temperature down some, and have been thinking about getting a powerhead for better circulation. Any help is appreciated, I don't like seeing my fish in distress

 

[Matt68005]

Shes trying to even out her swim bladder by taking in and exhaling air from her stomach, much like we (must) yawn and pop our hears to keep an even equilibrium in our ears.
Goldfish must be fed very small amounts of sinking pellets, they have very small stomachs, and gulping at the surface leads to stomach/swim bladder problems, we see it all the time.

 

[OneTwoRedBlue]

Shes trying to even out her swim bladder by taking in and exhaling air from her stomach, much like we (must) yawn and pop our hears to keep an even equilibrium in our ears.

Why do you think she'd be doing this every day? Sometimes she does it so much that she's unable to sink naturally, and will float at the top of the tank unless she actively swims down against her buoyancy.

Goldfish must be fed very small amounts of sinking pellets, they have very small stomachs, and gulping at the surface leads to stomach/swim bladder problems, we see it all the time.

I thought it was floating pellets that caused swim bladder problems? I soak the pellets in tank water for a few minutes to make them easier to eat and only feed as much as they can eat in a couple of minutes.

 

[Matt68005]

You dont need to soak them you just need to keep the food below the waterline, thats what i meant use sinking pellets....
Fancy goldish are just prone to this, i think it has something to do with their breeding, you dont see it in koi or regular goldies and they gulp like crazy