clear film around my tank

Question
I  have a 30 gallon tank and i have this clear film all around it. I only have three gold fish but two of them are really big and  i had them for a year. I purchase everything you could imagine to get this film out but nothing works. My tank is plastic and my husband changes the water twice a month but we cannot get that film out at all. I am seeing that my fish is not happy with there living conditions so please help me and my babies. if you could just give me some points on how to keep it clean all help you give would be appreciated

Answer
Sounds like an excessive amount of protein in the aquarium, the best way to remove this is to take a solution of vinegar and water (4 parts water, 1 part vinegar)and soak the tank it it for about 20 minutes, this will get rid of the protein particles inside the aquarium.  Make sure you rinse the aquarium very well with warm water prior to adding the fish back into it.