20G Community Tank

[kenkat]

I have 9 neon tetras, 9 corydoras and 3 sparkling gourami in a 20 gallon tall tank with sand substrate and some plants from petco and driftwood. I've had the tetras since Saturday. I got the 9 corys and 3 gourmi in the mail yesterday and put them in the tank. At first, everything seemed fine. The corys were swimming to the top at times for air but were flying around and being active and then would rest for a bit. This morning I found 5 of my corys dead. The tetras are and gourami seem perfectly fine but the remaining 4 corys are pretty inactive as of now.

 

[Byron]

I have 9 neon tetras, 9 corydoras and 3 sparkling gourami in a 20 gallon tall tank with sand substrate and some plants from petco and driftwood. I've had the tetras since Saturday. I got the 9 corys and 3 gourmi in the mail yesterday and put them in the tank. At first, everything seemed fine. The corys were swimming to the top at times for air but were flying around and being active and then would rest for a bit. This morning I found 5 of my corys dead. The tetras are and gourami seem perfectly fine but the remaining 4 corys are pretty inactive as of now.

Whenever fish begin dying like this, always do an immediate massive water change, 75-80% of the tank. Use a conditioner but no other substances. One today, one tomorrow. This is basic "first response" to trouble as described here. Using a QT for new arrivals also helps to contain whatever this could be, if it is a contagion disease. May be any number of things.

Beyond the W/C's, how were the fish introduced? Any possible toxins in the water? Significantly different parameters (GH, pH, tempeerature)?

 

[kenkat]

I did a pretty big water change. I don't think there are any toxins as far as I can tell.

Nitrite 0ppm
Nitrate 5ppm
Ammonia 1.0ppm
PH 6.0
GH 75ppm
KH reads as 0 but my test only goes between 0 and 40 ppm so not sure

The ammonia surprised me since I was pretty sure that the tank was cycled. I put a sponge that was used in a previously cycled tank and put in ammo lock and am monitoring. The corydoras still seem pretty weak. The neon tetras and the gourami seem fine as of now.

 

[kenkat]

One of my tetras just died. This is the second time I have gone through a tank having thought everything was cycled and while the other fish in the tank are still alive I am starting to think that fish keeping just is not for me.

 

[seangee]

did a pretty big water change. I don't think there are any toxins as far as I can tell.

Nitrite 0ppm
Nitrate 5ppm
Ammonia 1.0ppm
PH 6.0
GH 75ppm
KH reads as 0 but my test only goes between 0 and 40 ppm so not sure

The ammonia surprised me since I was pretty sure that the tank was cycled. I put a sponge that was used in a previously cycled tank and put in ammo lock and am monitoring. The corydoras still seem pretty weak. The neon tetras and the gourami seem fine as of now.

In post #7 you mention a pH of 7.2. This is a significant difference from 6.
With a KH of 0 you really need to keep on top of your water changes to keep the pH stable, I suggest 75% per week.
A pH of 6 and KH of 0 is not a problem (my KH is 0 and pH is closer to 5) but here is why it is important.

• At a pH of 6 most of your beneficial bacteria will die. Not a big deal if your pH stays at 6 because ammonia exists as ammonium in acidic water. Ammonium is not poisonous to fish.
• But if your pH goes up to 7 the ammonium converts to (poisonous) ammonia and you have no BB to deal with it.

That is an over simplification but the best way to protect against such swings is to do significant water changes every week so that the pH in your tank stays close to what is in your tap. To measure the pH from your tap water let it stand in a glass for 24 hours and then test it. The other protection is to have lots of plants. Plants will use whatever is available from ammonia and ammonium, so if you have enough of them you do not need to rely on BB to remove them.

I would not use ammo lock. This does not change @Byron's suggestion that the first response to any emergency is to do a large water change, but it highlights that it is important to keep your tank water as close as possible to your tap water to avoid big swings when you do have to do a large change.

Of course we cannot rule out any of the other possible causes Byron mentioned - but this is important for you to know.