please help

[jane]

we have had a tropical fish tank for 2 years now, and today my husband
has cleaned it out as he always does, we have been out for one hour and
come back and all the fish are at the top of the tank and look like
they are gasping for air, we have a couple of fish that are lying on
the bottom upside down - they look like they are suffocating, what have
we donw wrong - this has never happend before, we have a 4 ft tropical
tank with commiunity fish in it

[Steve]

jane wrote:
> we have had a tropical fish tank for 2 years now, and today my husband
> has cleaned it out as he always does, we have been out for one hour and
> come back and all the fish are at the top of the tank and look like
> they are gasping for air, we have a couple of fish that are lying on
> the bottom upside down - they look like they are suffocating, what have
> we donw wrong - this has never happend before, we have a 4 ft tropical
> tank with commiunity fish in it
>

Assuming that you're not putting us on:

There's something wrong with the water. Possiblities include:
- The buckets you used for maintenance had soap, detergent or something
else in them.
- Contaminated hands or impelements were used in maintenance.
- You forgot to use dechlorinator in the replacement tap water.
- You used way too much dechlorinator or other chemical.
- You've recently painted the room, or other solvents are in the air,
entering aquarium.
- Distant possibility is, that your water supplier switched from
chlorine to choramine. This requires a chloramine-specific
dechlorinator, although I think most will handle this job.
- etc

Solution:

Use non-contaminated implements to perform a near-100% water change.

Steve