Emergency Tank Maintenance

I recently added several fish to my aquarium; three Banggai Cardinalfish and a tiny Firefish Goby. The cardinals have been doing great. They love frozen mysis shrimp and live brine shrimp. They haven’t taken prepared foods yet but that may change over time. The firefish has presumably died now, a couple weeks later.

She was eating brine shrimp for a few days. But then she just disappeared, hiding somewhere in the rockwork. I say that she is presumably dead because when I checked ammonia this evening I found that its level had spiked to 0.4 mg/L. I haven’t discussed chemistry in detail yet but know, that for ammonia, the safe level is 0. This is going to start causing the fish not only stress, but lesions, and even death.

I can’t un-kill the fish, nor is there a fast way of removing ammonia from water, so instead I need to do damage control. The first part of this is a tear-down of the rockwork to try to find the carcass so as to get rid of the thing producing the ammonia. This is stressful for the fish, but also for me. Any time I put my hands in the tank there are risks involved for everyone. When tearing down the rockwork I risk injuring snails or crabs, potentially amplifying the ammonia load. The tear-down also disrupts a lot of tunnels that have been made under the rocks. There are also risks for me, which is going to be a future topic.

Unfortunately, the tear-down was not only stressful, but also fruitless. No carcass was discovered. I have no way of knowing what killed her but it is possible that her body is inside one of the rocks, where I can’t see it. Reef rock is extremely porous and has internal cavities which are much too small for a person to investigate. It is also possible (and this is my guess) that her carcass was discovered by the pistol shrimp and dragged into his tunnel network.

At this point I’m forced to try to bail out the ammonia as it is produced. This means that I’m currently filtering water to do an emergency late-night water change. A water change is simply removing some percentage of the tank water and replacing it with new, clean, water. Water changes are no trivial amount of work, and they are made vastly easier if spread out over a few days.

I’ll be doing a 10% change tonight as filtering water is an hours-long process, and it’s getting late. Tomorrow morning I’ll check ammonia levels again; if they aren’t at 0 I’ll do another change. I’ll be doing this daily until the tank scavengers finish consuming the carcass and nothing is left to produce ammonia.

I’m sad that I wasn’t able to provide a safe environment for a new fish, and it’s also unfortunate that I have no way of knowing what killed her, but it’s an inevitable part of the hobby. I hope that as time goes on I can get better at keeping new fish alive but a certain amount of it is always out of my hands.

For now I’m bailing out a boat and hoping the hole is smaller than the bucket.

Addendum: After several days of frequent ammonia tests and a few water changes the ammonia has returned to undetectable levels. There were no further deaths, and the ammonia never reached a truly toxic level; it was just bumping against it the first night.