HELP ASAP!

[missmarine]

i have a two guppies and one of them is sinking to the bottom, looks dead, then has like a seizure and starts swimming upside down then going up and sinking back down on his back. I don't understand what's wrong with him. He doesn't want food, and the other fish is perfectly fine.

any advice before he dies on me?1

[MGDMIRAGE]

More information? Ammonia, Nitrite, Nitrate, PH.

Have you done any large water changes lately?

[Rbishop]

New stock..long established tank?