SHOCKING! Two tigers dead.

[Quartermain]

Not the happiest day of my life.

I take 1 hour break every afternoon from work and since I live close I often come home for left overs. It also gives me a chance to feed my fish. Today I came home and my 20gal tank with 4 Tiger Barbs, 2 Gold Barbs, 1 Paradise Fish and 1 Clown Pleco had a rather thick film of clear white slime on the surface. I had just the day before removed two bags of carbon from the Fluval 204 filter. It appeared to be an unusually thick layer of protein scum. I had to break the surface to feed the fish and much of the scum crumbled into the tank. No big deal, I thought.

When I came home at around 5:00pm Two of my very Healthy very Happy Tiger Barbs were DEAD! Both had the white protein crumbles clinging to their corpses.

Although there is no way for me to know for sure how they died the presence of particles on their gills tells a tale. I suspect that these two fish in particular breathed particles in through their mouths and exhaled them through their gills, rather than spitting them out as the other fish may have done. The particles stuck in the gills and they suffocated.

Can I blame the protein scum on the filter? If so what can I do to minimize it in the future. I do have a general problem with algae in that tank. Will a UV Sterilizer help? Any help is much appreciated!

[Watcher74]

It appeared to be an unusually thick layer of protein scum. I had to break the surface to feed the fish and much of the scum crumbled into the tank.

By this do you mean that the entire surface of the aquarium water had a "scum" covering it?

If so maybe the scum was inhibiting the oxygenation of the water? If the fish were trying to obtain more oxygen by getting close or breaking the surface then that might explain the presence of the particles found on them.

[Quartermain]

The film was covering the entire surface but the fish were only exposed to the film after I put my hand in the aquarium to feed the Pleco. That stirred up the film and for a minute it looked like a blizzard. It was pretty intense. I tried to scoop as much of it out as I could with a small net. I got quite a bit of it.. not enough though, obviously.

I doubt there is a lack of oxygen in the water. All the fish look healthy, they're not struggling to breath, and they're not dodging to surface. The scumb formed within 48 hours after I removed the carbon bags from the canister. Only a very thin layer existed yesterday when I fed the fish at noon. The only other thing I can recall doing is dosing a larger than ussual quanity of Flourish Nitrogen and Iron becuase my N03 levels were dipping below 5ppm and my Fe level was not registering in the Hagen test kit that I use.

No, I'm fairly convinced about what killed those two fish. What I'm wondering now is how do I control this?

I went to Bigals.com and purchased a Fluval surface skimmer. My hope is that this will prevent the build up but it doesn't fix the core problem. But does anyone have any experience with these in a planted aquarium? Do they cause excessive surface agitation? It was a cheap thing ($8.00) so I'm going to give it a try anyway but if you have any experience my ears are wide open.

Also, does anyone think that a UV Sterilizer might do some good?