Fish Acting Very Strange

[chris_ba1212]

Hey all i'm new here but really worried about the fish in our tank.

We have a varied selection from tetras to clown loaches and a couple of plecs.

Basically i got in from work today and found over half the fish at the top of the tank as if gasping for air. Even the top plecs that are always at the bottom hiding were up there. I have some mollys including some babies these were there two along with both my angle fish a few barbs and a selection of different tetras. The only other things in the tank are 3 silver dollas, 4 gorramis, 3 clown loaches and a golden loach. No new fish have been added for about 5 months and i change a 3rd of the water every 2-3 weeks. Last change was about 4 days ago.

The only time i saw this before is when we added a red claw crab to the tank a lot of the fish were scared and were just trying to get away.

The only change i have made that i think could affect anything is last water change i added some poly filter pads to my filter as the old ones were shot but they were genuine fulval ones.

I have a fulval filter working fine and a long air stone adding air to the water. The tank is almost 250 liters.

I'm about to do a water test but any other suggestions?

 

[glolite]

Did you change the poly pads? If so did you throw the old ones away?

It would be helpful to know the water stats too.