Fish died all at once while cleaning

[Fierce]

Good day everyone,

I had a 30G saltwater tank running for at least 1 year with no issues whatsoever. One day I saw my watchman goby, which I had for around 8 months, turn white slowly, and then suddenly died. At the time I did not think much of it. 2 weeks later, I saw one of my fire goby gasping for air and not eating, in a panic, I started to do a 50% water change because I thought the water quality was not good, which I usually change it once a month. While doing some water changes, I also decided to clean the sandbed, which I almost never clean because it is hard to since rocks are in the way and I can't clean it much without moving some corals. While cleaning it, I suddenly noticed that suddenly, all the fish started gasping for air and then all fell to the sandbed at the same time. After around 5 minutes, they all died. I had some shrimp and some corals, but they weren't affected much. I moved them to a new tank to be sure, and until now they're doing fine.

I had:
2x Clownfish
1x Watchman Goby
1x Fire goby
2x Yellow Wrasse
2x Cleaner Shrimp
Multiple Turbo Snails
Multiple Narcissus Snails
2x Torch Corals
1x Frogspawn
1x Blastomussa

This was around 3 months ago and I stopped reefkeeping for a while because I was feeling down, I just kept up with the maintenance of the leftover corals and shrimps but now I want to get back to it again, but before I do, I want to know what I did wrong. While researching, I saw in the forums that it seems like I disturbed the sandbed which had a lot of ammonia buildup, but I'm not sure if this is really the case. If so, how do you usually clean the sandbed, especially the ones with stuff burried deep without having to move some rocks and corals, really want to know how others do it so that this situation could be avoided again. I also want to add that after the event, I checked the ammonia levels using an API test kit and the levels were normal (0.25ppm).

Thank you in advance for any input :))

 

[cakefullofjake]

Yeah, honestly, probably was your sand bed ammonia is what kills fish the fastest. When doing water changes use a tube that has a cylinder at the bottom to safely get deeper in the sand without having to release as much ammonia into the water column. How often did you do water changes? That sand bed must’ve been really bad to tank your tank after a cleaning

 

[jbisDVM]

It could be that disturbing the sand bed caused an ammonia spike but it seems that your test kit ruled that out. The other possibility is that trapped gas was released by the sand bed. I’ve read before that hydrogen sulfide gases build up in the sand as a result of anaerobic bacterial metabolism. If enough of those bubbles are released it can be toxic. I also sift my sandbed frequently to prevent excessive build up and when I’m vacuuming during a water change, I’ll only do a portion at a time.

In my opinion, I think the trick is to either choose whether you will never touch the sand bed, or do it frequently enough that there isn’t time for excessive build up of gas and detritus. It seems that anything in between can lead to disaster.
I’m sorry that happened and I hope your second attempt is successful!

 

[Mark Goode]

One more vote for sand bed.

 

[Fish Fan]

Good day everyone,

I had a 30G saltwater tank running for at least 1 year with no issues whatsoever. One day I saw my watchman goby, which I had for around 8 months, turn white slowly, and then suddenly died. At the time I did not think much of it. 2 weeks later, I saw one of my fire goby gasping for air and not eating, in a panic, I started to do a 50% water change because I thought the water quality was not good, which I usually change it once a month. While doing some water changes, I also decided to clean the sandbed, which I almost never clean because it is hard to since rocks are in the way and I can't clean it much without moving some corals. While cleaning it, I suddenly noticed that suddenly, all the fish started gasping for air and then all fell to the sandbed at the same time. After around 5 minutes, they all died. I had some shrimp and some corals, but they weren't affected much. I moved them to a new tank to be sure, and until now they're doing fine.

I had:
2x Clownfish
1x Watchman Goby
1x Fire goby
2x Yellow Wrasse
2x Cleaner Shrimp
Multiple Turbo Snails
Multiple Narcissus Snails
2x Torch Corals
1x Frogspawn
1x Blastomussa

This was around 3 months ago and I stopped reefkeeping for a while because I was feeling down, I just kept up with the maintenance of the leftover corals and shrimps but now I want to get back to it again, but before I do, I want to know what I did wrong. While researching, I saw in the forums that it seems like I disturbed the sandbed which had a lot of ammonia buildup, but I'm not sure if this is really the case. If so, how do you usually clean the sandbed, especially the ones with stuff burried deep without having to move some rocks and corals, really want to know how others do it so that this situation could be avoided again. I also want to add that after the event, I checked the ammonia levels using an API test kit and the levels were normal (0.25ppm).

Thank you in advance for any input :))

I'm sorry to hear about your fish losses. I think because you tested your ammonia and it was ~0.25 ppm, which is not a dangerous level of ammonia, and likely test kit error, this situation was caused by hydrogen sulfide. Hydrogen sulfide can form in anoxic (no oxygen) regions of your tank, like in the sand bed. When you suddenly disturb the sand bed after a a long time, you can release hydrogen sulfide gas, which is highly toxic. Here's RHF's article on Hydrogen Sulfide:

Hydrogen Sulfide in Reefs

Hello, I have been using an anaerobic reactor to heavily reduce nitrates, it works amazing but I am having troubles dialing it in. Most of the time, the effluent is 0ppm nitrate but there is a definite detectable sulfur odor, which I presume to by hydrogen sulfide. This is only evident in the...

www.reef2reef.com

To minimize the risk of hydrogen sulfide poisoning, clean just a small portion of your sand bed on a regular basis, so over time it's all turned over periodically, but not all at once. You can also get some sand moving critters to help.

Good luck going forward!

 

[Featherweight]

Sounds like you had stuff on your hands to me

 

[Randy Holmes-Farley]

Yeah, honestly, probably was your sand bed ammonia is what kills fish the fastest. When doing water changes use a tube that has a cylinder at the bottom to safely get deeper in the sand without having to release as much ammonia into the water column. How often did you do water changes? That sand bed must’ve been really bad to tank your tank after a cleaning

Why would you think there is ammonia in the sand? Seems very unlikely to be that. If it is the sand, hydrogen sulfide is the likely culprit.

Ammonia is not nearly as toxic as most
people think, and I don’t how it could accumulate to the massive levels needed in the sand to then be lethal once diluted in the tank.