New Cory Cats are Dying- Help!

[sakurablossom]

This is my first post. We have a fairly new lo-tech, lo-light dirted heavily planted tank. (2 months old, fully cycled). We started to add fish in the tank last week. 10 cherry barbs, 3 male Bosemani Rainbowfish, 2 Siamese Algae Eaters, 2 Bristlenose Plecos, 6 Amano Shrimp, 3 Netrite snails and a number of Malaysian Trumpet snails. The tank is 120 gallons. The substrate is mineralized topsoil with Eco-Complete cap. We have tons of plants, a large piece of driftwood and natural rocks (slate and Texas holey rock). Our ammonia is 0, nitrite is 0, and nitrate is .5. Our ph is 7.4, hardness is 10. The temperature during the day is around 81-82F and 79-80F and nighttime. (We live in AZ so that is as low as we can get our temperature down in the summer).

About a week ago, we added 5 Julii Cory Cats. Since then, two have suddenly died. A couple of them have gone up to the surface of the water, hung up there for awhile and then floated back down to the bottom of the tank. We are assuming these are the two that died. They have both done it about a day before they died. They have no abnormalities with their appearances. The three that are still alive, spend their day in the back corner of the tank where it is darker,sleeping. Their main diet is shrimp pellets. I am not sure if they come out at nighttime and eat any of the algae wafer and pleco pellet we also have in the tank. We are wondering if there is something in our tank causing their deaths or if maybe we just got sick cory cats. And should we keep the other three and watch how they are doing or return to the fish store? If it is something in our tank casuing their deaths, then I don't want to keep them and have them suffer. Does anyone have any ideas? Thanks.

[Corycory]

Sorry to hear about your corys.

Do the rest of them go to the surface?

Are the nerite snails and shrimp doing ok?

How did you acclimate the fish?

I do think it's quite a bioload to add in such a short period of time but it's a large tank and well planted and if you exclude the possibility of an ammonia/nitrite spike then it could be something else.

One reason could be if during transport, if kept in the bags for long, some corys excrete a toxin which can poison themselves and maybe some of them didn't make it.

Additionally, I'd just do several large water changes in case the soil is releasing any chemicals.

Also, oxygen levels. Dirted tanks upon setup have very high organics that start breaking down using lots of available oxygen. Make sure there's enough surface movement and fish are not gasping, breathing heavily.

And another issue, anaerobic soil due to high organic levels and low oxygen. Corys are in immediate contact with the substrate and they can be affected by soils producing hydrogen sulphide in anaerobic substrate rather than co2 in well oxygenated substrate. Is the substrate "bubbling". Are plant roots black or normal?

Also, check Ph and Kh and make sure the Ph is not dropping/fluctuating and the Kh is at least 2 at any given time.

[sakurablossom]

The only time I see the cory cats go up to the surface is the day before they die.

So far, the snails and shrimp are doing good. The shrimp have been working as soon as we added them to the tank.

We dripped acclimated the cory cats for an hour.

We haven't had any ammonia/nitrite spikes. We have two canister filters.

They were in transport for about 30-40 minutes. Could that have been too long for the cory cats?

We have airstones constantly running in the tank due to our higher temperatures to make sure there is enough oxygen in the tank.

The substrate is not bubbling and the plant roots are normal color. Are there ways to stop anaerobic soil from happening? We bought the Malaysian Trumpet snails for that purpose. But I do see them out of the soil a lot eating algae in the tank. They have been like that from day one. I try to also poke at the dirt once a week, but with all the plants and decorations, I cannot get to most of the dirt. Could that be an issue? I figured that the plants roots would help stop anaerobic soil from happening.

We checked the ph to make sure we didn't have a ph crash. It was at 7.4. We didn't check the kh since we have hard water but we can check that.

My husband said that the dead cory cat he took out yesterday seemed to have a bubble under his skin in his stomach region. Does that mean anything?

[Corycory]

You could have been unlucky and got diseased corys. I listed anything else I could think of.

Soil tanks can go anaerobic at the start because the soil is too rich. It can go away in time because most of the organics will eventually break down, lots of oxygen and poking the soil more often helps, even every day at the start. It's worth a try but its only a speculation based on what you see in the corys. I'd do it as a prevention. High temperatures don't help with oxygen as the water can't hold it.

As for the bubble on the belly, without a picture I am not sure, some sort of swelling?

It's impossible for me to tell what it is. The best shot at this stage is lots of water changes, even with a bit cooler water to drop the temps down, poke the soil and keep the oxygenation at least until the weather is cooler.

And yes, 30-40min in a bag is enough for the corys to poison themselves. Some corys are more susceptible than others, not sure about your corys as I've never had them. I particularly had that with my sterbai, they did gasp at the surface and were obviously stressed when I finally put them in my tank. They had lost their colour and all but they recovered within a few days.