Cardnal fish dropping one after another

Arruna · Jan 1, 2021

Hello!

In my 35 gal tank, I have a clown fish, 2 large turbos, 1 emerald crab and nas snails, and 2 peppermint shrimp.

About a month ago I added 4 cardinals. 2 ate well, 1 wasn't taking to food and one was passive but eating a bit. About a week later one just vanished in the night. I assumed he passed and was the one not eating and the CUC took care of him. The next week another one vanished. Same way. Went to bed at 10pm by 7am he was gone. No where. OK another die off right was prob the passive one? The remaining two were the good eaters. Fat little guys. Another week or so passed. No change in the tank. Everyone is eating good. This morning I found one of the carnals dead almost fully eaten. The snails and peppermint were finishing him off.

Now he was healthy, eating, active. So now I'm convinced something in my tank is taking out the cardinals as they are slow unlike the clown. (The clown and cardinals hang out all day in plain view. No aggression has ever been seen)

Can anything I listed be the killer? I am also concerned I may have whelks snails as I see some "nas snails" chilling on rocks. Do you think they could be killing the cardinals?

EvanDeVita · Jan 1, 2021

Arruna said:
Hello!

In my 35 gal tank, I have a clown fish, 2 large turbos, 1 emerald crab and nas snails, and 2 peppermint shrimp.

About a month ago I added 4 cardinals. 2 ate well, 1 wasn't taking to food and one was passive but eating a bit. About a week later one just vanished in the night. I assumed he passed and was the one not eating and the CUC took care of him. The next week another one vanished. Same way. Went to bed at 10pm by 7am he was gone. No where. OK another die off right was prob the passive one? The remaining two were the good eaters. Fat little guys. Another week or so passed. No change in the tank. Everyone is eating good. This morning I found one of the carnals dead almost fully eaten. The snails and peppermint were finishing him off.

Now he was healthy, eating, active. So now I'm convinced something in my tank is taking out the cardinals as they are slow unlike the clown. (The clown and cardinals hang out all day in plain view. No aggression has ever been seen)

Can anything I listed be the killer? I am also concerned I may have whelks snails as I see some "nas snails" chilling on rocks. Do you think they could be killing the cardinals?

I would put my money on the emerald crab. I had a similar problem, and the killer was my sally light food crab.

Dkmoo · Jan 1, 2021

What are your tank parameters? Ph/ammonia/nitrite/nitrate, specifically. Also tank age? Do you have a picture? Want to see how "mature looking" the rockscape is. What are your primary waste export mechanism?

IMO your other livestock are not the culprit. It is extremely rare that a CUC can actively be the predator and kill a healthy fish of similar or larger size. It is more likely that something caused then fish to be unhealthy/dying/dead and your CUC is just doing their Job

Without knowing the details above, my first hunch is that you added too many fish at the same time and the sudden increase in both feeding and waste was too much for your nitrogen cycle to handle and the fish died from ammonia or nitrite poisoning.

Arruna · Jan 1, 2021

Ammonia is 0
Nitrite is 0
Nitrate is about 10
Ph 8.2-8.4

Added pics above

This tank is fairly new. About 6 months?
But we took the rockwork from another one of our tanks that we took down that was about 3 years old. (We wanted to upgrade the size and move it) and added maybe 1 new rock piece that was wet rock from the LFS.
The sand was new and the water was 75% new and 25% from my 150gal aquarium that has been up and running for 3 years. (Those water parameters were all 0 when tested before taking some of that water)

If it was may water, wouldn't my CUC be effected too? I havnt noticed any die off of them. Thankfully!

Dkmoo · Jan 1, 2021

Yeah that looks fairly new. With ammonia and nitrite, since it's 0 now that means your tank does have nitrifying bacteria, it probably just wasn't enough to process the sudden increase fast enough. My suspicion is that unless you "catch it in action" as in right after all 4 cardinals pooped, the elevated ammonia and nitrite probably are already processed by now. Since you only have 2 left, their poop isn't going to create as large a spike so if these two survive then that is most likely your cause for the first 2 dying.

As for why the rest of your livestock seem unaffected - they probably were. The thing is, the elevated ammonia/nitrite conditions probably only lasted a few hours, the existing live stock were probably healthier bc they didn't have the stress of new tank and moving so they outlasted the condition. The 4 new fish were affected more due to stress, moving, new environment etc, the 2 weaker ones didn't make it.

The "waste profile" is very different between fish and CUC. The 1 clown generates a lot more waste than the rest of your CUC, so when you added 4 more fish, the total waste in your tank most likely increased by a factor of 3x to 4x at the same time, causing your nitrifying bacteria to not keep up and causing the temporary elevated conditions.

Arruna · Jan 1, 2021

Dkmoo said:
Yeah that looks fairly new. With ammonia and nitrite, since it's 0 now that means your tank does have nitrifying bacteria, it probably just wasn't enough to process the sudden increase fast enough. My suspicion is that unless you "catch it in action" as in right after all 4 cardinals pooped, the elevated ammonia and nitrite probably are already processed by now. Since you only have 2 left, their poop isn't going to create as large a spike so if these two survive then that is most likely your cause for the first 2 dying.

As for why the rest of your livestock seem unaffected - they probably were. The thing is, the elevated ammonia/nitrite conditions probably only lasted a few hours, the existing live stock were probably healthier bc they didn't have the stress of new tank and moving so they outlasted the condition. The 4 new fish were affected more due to stress, moving, new environment etc, the 2 weaker ones didn't make it.

The "waste profile" is very different between fish and CUC. The 1 clown generates a lot more waste than the rest of your CUC, so when you added 4 more fish, the total waste in your tank most likely increased by a factor of 3x to 4x at the same time, causing your nitrifying bacteria to not keep up and causing the temporary elevated conditions.

You think this would still be the case for the one I just lost today, or I guess last night? 3/4 ? One that was super active and eating well since the start, 1 month after they were added?

Dkmoo · Jan 1, 2021

Could still be if the elevated condition happen overnight - do you have any liquid bacteria that you can dose?

I know you said the rocks are from an old tank but they still look pretty "white" and new. Plus the sand is new so it probably still lacked the biodiversity needed to handle sudden waste increases (i do see diatom in the sand, another common sign of not matured biofilters yet)

If the last one still doesn't make it and you were able to dose additional bacteria, esp if its 0/0/10 now, then there may be other factors at play here.

Dkmoo · Jan 1, 2021

Also any physical signs of disease? Do you target feed the crab? Since rocks looks new if there's not enough food a crab might misbehave so let's rule out that possibility if you can keep the crab fed.

Edit: crab and shrimp. Snails cannot catch a live fish no matter how weak or sick the fish is. A starving crab or shrimp might.

Dkmoo · Jan 1, 2021

Id also keep a close eye over the next 48 hrs on your parameters. The new fish dying is going to test your nitrogen cycle from the rotting carcas and CUC suddenly eating a lot (more poop)

Arruna · Jan 1, 2021

Dkmoo said:
Also any physical signs of disease? Do you target feed the crab? Since rocks looks new if there's not enough food a crab might misbehave so let's rule out that possibility if you can keep the crab fed.

Edit: crab and shrimp. Snails cannot catch a live fish no matter how weak or sick the fish is. A starving crab or shrimp might.

No sign of disease. I just dosed some bacteria. And I only see the crab every few days. I'll be sure to spot feed when I see him

Dkmoo · Jan 1, 2021

Arruna said:
No sign of disease. I just dosed some bacteria. And I only see the crab every few days. I'll be sure to spot feed when I see him

Good luck! I hope your last little guy makes it!

I'm at work now but ill brainstorm some additional factors that may be at play here tonight to help you diagnose the issue.

Arruna · Jan 1, 2021

Dkmoo said:
Good luck! I hope your last little guy makes it!

I'm at work now but ill brainstorm some additional factors that may be at play here tonight to help you diagnose the issue.

Thank you so much. Its really appreciated!

JumboShrimp · Jan 1, 2021

Given how new the rocks appear, your transfer from one tank to the other might have benefitted by a whole bottle of bacteria. Also as I good idea for the future— even years from now (your next tank upgrade)— start several mesh bags going in your sump with rubble-rock or something else porous; then when you transfer tanks again, you will have ‘bags’ of excellent bacteria to drop in. Best wishes going forward!

iamacat · Jan 1, 2021

Agree with the others. Nothing in your tank would wipe out fish like that. You experienced a very large bio load increase when the 4 cards were added. You’re system is doing a balancing act while it matures, you just tipped the scales. The stress from ammonia at introduction could have weakened the immune response and the fish succumbed to something it might have been able to overcome. Water changes and some patience, things will be fine

Dkmoo · Jan 2, 2021

Some more thoughts. hopefully can help you going forward -

majority of time fish death is due to stress that weakens their immunity/general health as others have mentioned. what we talked about before are some of the most common factors such as ammonia, new talk acclimation stress, etc. Below are additional stress-inducing factors to keep in mind

1) at the LFS - is the fish from a holding tank or a community display tank? holding tanks are typically very crowded with very little rock work that can offer hiding spots, which cards love
2) is the card wild caught or aquacultured? wild caught are typically a lot more stressed and have far lower survival rate. I would highly recommend against wild-caught ones if you plan to buy more - they are already an endangered species from over predation.
3) hiding spots - their natural habitat is the indonesian reefs so they need a lot of caves, overhangs and just general "stuff" to swing thru and around in. I see you have a big main open cave but couldn't tell from the pic if you got other smaller nooks and crannies that it can hide. My tank is a full mixed reef (see my tank build thread) and my card mostly prefer areas with smaller caves he feels cozy in, and hangs around near my big wavy soft corals. Without adaquate hiding spots it can build it gradual stress. I'm not sure if you plan to add corals later, and i hate to suggest you redo you rock work, but maybe just take that loose purple one rock and put it inside the big cave to make multiple smaller caves? Also whats the personality of the one remaining card? is it more or less staying in one spot in the open? or is it venturing around and looking for a good hiding spot? their behavior can sometimes give u an indication if its stressed or not. A happy cardinal that's "settled in" swims around and thru things to explore but always goes back to the favorite "home" spot. a card that just stays in one spot could be stressed/scared to explore around.