Goldfish help

[Mall0ryKnox]

I got my goldfish from a fair a year ago and (s)he has been an awesome fish... but lately ... not so much. I haven’t seen it eat in a few days, it used to swim up and grab all the food at feeding time. Now it looks at me like, “get out of here”.
It’s staying by the air bubbles and then goes over by the heater, and back and forth. It’s been floating on its side too! I have a 15 gallon tall tank (pics shown) I don’t want this fish to die. I don’t know the water levels, I have to bring a sample to the pet store tomorrow. I just did a 50% water change yesterday. What else could I do to save this beauty?

 

[SaraB]

What are your water parameters? Number please not just "goid" or "fine".
Goldfish need large tanks, they get huge and create a lot of waste.
What is your temperature? Do you have a filter? Do you have an airstone?

 

[Mall0ryKnox]

I’m bringing a sample to the pet store today to get the water levels… There is a heater, there is an air stone. My thermometer says 76, the fish has been in this same tank for a year now, I haven’t done anything differently. I do plan on getting a bigger tank soon. It’s swimming around at the top of the tank today, I was checking on the fish throughout the night. A couple times s(he) was on its side but flipped back over when I came around.

 

[Mall0ryKnox]

Also, I do regular water changes. Weekly, sometimes bi weekly. About 25-30%

 

[SaraB]

Ok. Goldfish like cooler temperatures so you can take out the heater.
Your water changes need to be either bigger or more frequent. Think 25% twice a week or 50-60% once a week.
You should see a bit of improvement, but a lot more once you get a bigger tank.

 

[Mall0ryKnox]

Thank you very much I will take your advice.

 

[Mall0ryKnox]

I just got home from the pet store to find that the fish had passed away ???