hypoxia problem

Question
QUESTION: hi i dont want to bother you bu this question is an emergency so can you please help me and answer this question.
for about 2 weeks ive been seeing my fishes hanging out at the surface of the water, just swimming around and sucking at the surface as if they were eating. i have 1 goldfish about 2 inches, 1 green cobra guppy about 1 inch and 1 crayfish about 2 and a half inches. they are in a 3.5 gallon plastic container and i have 2 filters operated at once, they are using the same airpump made for 5-10gallons of water. i do my weekly cleaning(gravel vaccuming, algae scraping, water changes and i feed them once a day. the ph level is 7.4 and nitrite levels are 0ppm, i would expect the ammonia to be 0ppm too since ammonia breaks down to nitrite but i dont have a nitrate test kit. my question is are my fishes experiencing hypoxia, or are goldfishs and green cobra guppy top dwellers. should i buy a new, stronger air pump to increase airation? i know its too much information but i thought its what you need to know in order to help me.

ANSWER: I would change about 50% of the tank water and see if they calm down.  Fish that hang at the surface are usually trying to gulp air which means that their tank is toxic.  The culprit is usually ammonia so changing the water should help them.... dave

---------- FOLLOW-UP ----------

QUESTION: yea i did a 20% change at the morning and they seemed to be doing the same thing. but wont doing a 50% change send me through a mini8 cycle, because that happened to me once. also could i help them out a bit by getting a more powerful air pump?

Answer
You can have the water tested to see if the water chemistry is out of alignment.  If the water chemistry is ok... then you do not have to change the water.  You can try to add more oxygen and see if they settle down.... and check your temperature.... warm water holds less oxygen then colder water... what is the temp in the tank???? dave