Help! Fish are dying and I have no idea what is causing them to die...

[sjkali]

Here's a little background information...

I have a 20 gallon freshwater aquarium, with a 50 gallon Aqua Clear filter. I currently have Mollies, Platys, Neon Tetras, and Cory Catfish- A total of 15 fish. The tank does not seem to be overstocked, most of the fish are on the smaller side and not anywhere near full grown. I do regular weekly partial water changes, and do not overfeed the fish. The temperature in the tank has remained a constant 82 degrees.

Over the past few months, I had noticed a little bit of a green algae problem. About a month ago, the algae problem seemed to be getting worse along with increasing cloudiness in the water. After doing some testing, I realized that my ammonia levels were out of control at 4 ppm. Prior to this, I had never seen any significant problems with any of the levels in the tank. My filter media had been well established for approximately a year and I originally did a fishless cycle to make sure that I had a strong biofilter.

After talking to someone at the local fish store (family-owned, well-established and credible), we came to the conclusion that something had caused my original biofilter to die off, therefore not effectively removing the ammonia in the tank. At this point, I did a 90% water change and cleaned everything in the tank along with replacing the filter media including a new biofilter from a friend with a well established aquarium (biofilter has been in friends tank for over a year). The biofilter was transported in aquarium water within the period of a half hour, therefore no chance of any of the good bacteria dying off.

So, over the past few weeks I have had multiple fish die unexpectedly. All of the levels have essentially remained the same. The ammonia has been at .25 ppm, ph is at 6.8, nitrites are at 0 ppm, and nitrates are at 5 ppm. It appears that the nitrogen cycle may possibly be stalled or something else might be occurring. There is also a whitish film forming on the glass.

I always use dechlorinator when adding new water to the tank. I did test my tap water and noticed that there is a slight bit of ammonia in it. I have used an ammonia lock product recently to make sure that any ammonia that was in the tank was not harmful to the fish.

I'm not really sure what to do at this point. Any help, suggestions, or advice would be greatly appreciated!

[Fishfur]

Any idea how long the ammonia was high ? It can kill in a very short time, and it can kill days later or weeks later, because it damages the gills. The fish have trouble breathing, become weak and die. Or they have internal damage from ammonia as well and die. Only takes a few days at ammonia levels as high as yours were. Fish are like any other animal. When they are feeling poorly, they hide it for as long as they can, because it makes them vulnerable. So by the time you see symptoms, it may be too late, or the fish is actually dying. And there is really nothing to be done for ammonia burn that's gone too far.

Does your test distinguish between free ammonia and ammonium ? Seachem's test does, API's test does not, so that .25 reading might only be ammonium and harmless.

Ammonium is bound chemically in the water. But free ammonia is not, and is what damages fish. High pH can release more free ammonia from the bound state, but that does not seem likely in this case, as your pH is not alkaline. I think your cycle is fine.

I suspect the deaths are due to the earlier ammonia exposure, and you may lose more, I am sorry to say. But new fish should do fine, given the new filter being established.

The ammonia in the tap water means the local water company adds ammonia with the chlorine, which forms chloramines. These last much longer than chlorine, so they kill more bacteria. Often added in summer, or after heavy rains, and it's not like they tell you about it.

What dechlorinator do you use ? If it is not Prime, I suggest you switch to Prime. It binds chloramines too.. and most of them treat chloramines, so that's not the only thing. It reduces nitrates as well, and is so concentrated, it lasts a very, very long time compared to most other products. I would not use anything else. Never makes the water foam up, as some do.

Amquel is not bad either, but Prime is, I think, the best brand out there.

Whitish film on glass is a new one on me. Is it soft ? Can you wipe it off easily ? Might, possibly, be fungal if that is the case. I'd wipe as much off as possible, then rinse out the filter media, as it will have been sucked into the filter. Is your tap water normally 6.8 or do you do something to lower the pH ? Is your local water hard or soft ? Have you tested GH and KH ?

Kind of scrambling for reasons here for the film. The only whitish film I have dealt with is from hard water, and normally only appears at the water's edge. Any chance of a pic ?