Fish all swimming upright?

Question
All of our fish have suddenly swam to the top of tank.  We have several clown loaches and they are swimming vertically. What could have suddenly caused the fish to all have the same reaction?

Answer
Hi Christina;

That is a very bad sign. It means there is a lack of oxygen in the water and/or there are toxins in the water causing them to be unable to absorb oxygen. They go to the top where there is the most oxygen and they will actually take air past their gills temporarily. Make a water change right away. Use a good water conditioner and be sure the new water is the same temperature as the old. Replace 25% now and then another 25% in 12 to 24 hours. That will reduce toxins and hopefully help them feel better. Add air with an air pump and an airstone to increase oxygen saturation so they can get as much as possible until we can figure this out. Parasites on the gills are possibility too so look for salt specks on the fins and body. Ich, a common parasite, can infect the gills first and cause these symptoms.

Now, if you can help me by answering a few questions;

How long has the tank been set up?
How big is the tank?
How big are the fish?
What other fish do you have in with them?
What kind of filter system?
What is the water temperature?
When was the last water change made?
How often do you usually make water changes?
How much at a time?
Have the fish been eating normally?
What do they like to eat and how often?

Let me know soon so we can hopefully find out what's wrong......

Chris Robbins