Ammonia Level = None detected
pH= 6-7

Tank size= 10 gallon 4 months
Filter= Aqua- Tech model 10-20
Water changed every two weeks 10%
two small goldfish
Before water is added at water change i use Tetra Aqua safe water conditioner.
No new fish or medicatin to tank
Fish are fed TetraFin Goldfish flakes.

One of my fish has a small bubble present on his bottom. He also has a bubble that is attached to a string looking thing hanging off of his tail fin. It is causing him to swim all crazy. He is still eating alot and swimming around. My other fish seems fine. What could be causing the bubbles?

Hi and welcome to the site.

First thing you need to do (or post) is test for nitrites and nitrates.
It is good your ammonia is 0, but we need to know what the other results are as well.
If you haven't tested them yet that is step one. If either or both of these are out of whack it could have something to do with the fish's health.

Next, I am sure if you have read the site that you are overstocked. GF don't go by the inch per gallon rule. It is 10 gal per "fancy" gf. 20 gals for each common.
So I would encourage you to change more water more frequently to help the quality until you are able to upgrade tanks.

We also need to know about the type of filter you have.
As well as clarifying the ph......is it 6 to 7 or 6.7????

Finally testing the tap water and posting those results are as well needed.

Onto the bubble. If you can get a picture of it, that would be ideal. CAn you describe it better? Is it clear or colored?
What exactly do you mean when you say there is something hanging off of it?
As well as making the fish swim funny, please give more detail on that.

Until you post back, I would encourage a water change of 30%.

How are the fish?