Goldfish swimming odd

Question
I have a baby biOrb  (4gal) aquarium with three faintail goldfish that I have maintained
with no problems for about a year now. Yesterday I noticed one of my fish was
bent on its side, on the bottom of the tank. It was gasping and moving its fins
sporadically and appeared to be twitching. I prepared for the worse, expecting
the fish to be dead this morning, however its condition seems to have improved
drastically. Its still swimming on its side, but the twitching has stopped and
it appears to be in control of its movements and breathing is regular. What is
wrong with my fish and how can I help it?
I don't know the ph ammonia or nitrite levels, and I replace 1 gal of water as it appears to need it.

Answer
Hi Katie;

The twitching may have been a seizure or muscle cramping. They really just need a bigger tank. Without enough room to swim and get enough exercise it's only a matter of time before they start having other problems as well. Each goldfish needs at least ten gallons in order to grow, thrive and reach their potential size of 6 inches or larger and to live a full life of over 10 years. Until they get a larger tank, change 25% of the water twice a week. It will lower the dissolved organic wastes and help them feel better and hopefully postpone some of the harmful effects for a short time. Here is a good web page about goldfish and what they need;

http://www.firsttankguide.net/goldfish.php

At Your Service;
Chris Robbins