I am pretty sure my tank is doing this. I have this really old tank, been sitting in the basement for years, so I cleaned it up and let the water cycle and added 2 fish, the both died that day . The water was fine and I had no idea what caused it. The next morning it has a clear film on the top, it is almost like a tin layer of rubber, i scooped it off with my net and gave it a few days to see if it would come back. It came back and now it smells pretty bad, I am wondering could it be the seal on this tank is just so old it is, i guess melting? (this is a tank from maybe 10 years ago, more or less) But it's not showing any signs of leaking. I'm really don't know what to do. any advice would be helpful.

OK, well, some questions to help solve this problem:

how did you clean out the tank, ie what chemicals, etc?

Is there a filter on the tank?

Did you dechlorinate the water before adding fish?

What ornaments are in the tank?

How long, and how, were you cycling the tank before adding fish?

I don't see how the tank could foul the water unless it had chemicals in it or something... hopefully you get this mystery figured out soon!

Do you have bubbles? I think that a film can form on top of the water if it doesn't get stirred around enough...

One gallon tank, washed the rocks just with tap water. cleaned the underwater filter with tap water, 1 plant don't remember what it's called (looks like grass), 1 hollow castle ornament I just rinsed it with hot water, I cleaned the tank w/ vinegar let it sit for around 2 hours then rinsed it out a few times. I had the water set-up for about a week with water from a different cycled tank. The water was cycled when I put the fish in. Yes, I did dechlorinate the water, a little over half the water was from a larger tank I have. It smells like burning rubber, which isn't very nice to have in my room lol.

Edit:spelling

did you say 1 gallon? 1 gallon isn't enough for 2 fish, not even for1.

I kno they were neon tetras i was moving them in to a five gallon, and putting a betta in the one gallon. It was just a quarantine tank.

If you were using new gravel then my guess is that something may be leaching out of if or the fine dust hasn't settled to the bottom of the tank. Try washing it again thoroughly and see if the film comes back.

Yea that's what I'm trying, *fingers crossed* I hope it's not the seal.

Just as i feared, the seal in my tank is comeing off, it's melting. It's too big of a mess i am just going to get a new tank, with this one i would have to get all the seal peeled off, and find new, for about the same price i can get a new one with a nicer frame. Thank you all.

One other thing: neons are tropical fish. there would be huge fluctuations in temp in a 1 gallon tank, which probably didn't help their situation!

sorry to drag this out, i just learned it was a 2 1/2 gallon (i thought it seemed larger than most 1 gallons), the seal did finally give out so it's off to the trash, i bought a new tank and a betta, well the betta isn't in it yet he is in a 1 gallon, the temp really had no time to set in for the 2 of them, the chemicals that the seal gave off killed them almost instantly. hopefully this tank will work for me. Thanks for the advice.

Good luck.

what an adventure..what size tank did you get and what fish will you get?

It was just a 1/2 gallon for my betta.

But now it is back on the new tank! It's not the seal, it is like goo, almost like when u put paper in water, yea, i am taking it to the lfs but i can't untill sunday, i was planning an doing a quick fix and just putting a lid, with some small holes in my five gallon to seperate my bettas. My mom doesn't think it is a good idea, b/c we won't b home and the lid gets knocked down they will fight and we might no longer have any bettas! Any ideas, i just right now have to get them through a fw days then i can worry about the other tank.