Paroon shark swimming weird

[Dharshan]

Hey guys... I need help to save my paroon shark. It's been a week a bought him and was totally fine n happy....but today since after noon he is trying hard to swim..he's been swimming upside down and not eating anything....and he is just 3inch long and he's become thin than before...
I have a quite big tank with 2 blind fan tail goldfish and 2comet goldfish and a pleco and few guppies and 2 paroon shark and one the paroon shark is sick ...and the tank has a sponge filter...
Pls help I really don't wanna lose him

 

[thrujenseyes]

OMG I sure hope you have the name wrong....
that should never be bought for an aquarium!!! They can reach 8 feet!!!!
If you have that correct I'd suggest to immediately take them both back!!!

That said, your stocking is very wrong.

How big is this tank? Is it cycled? And what are your water parameters?

 

[fluttermoth]

Do a large water change; drain the tank right down, leaving just enough water for the fish to swim upright, before refilling, making sure the new water is warmed and dechlorinated.

As thrujenseyes says these fish are not at all suitable for home aquaria. A sponge filter is not going to be powerful enough for the fish you have, which are mostly large, messy ones.

We do need to know exactly how big your tank is, and whether you've been testing the water.