Please help, cannot keep fish alive……

[kaleburn]

Hello, all. Absolutely devastated to report that I’ve had my reef tank now for over three months and have managed to kill all ten fish I’ve introduced into it. I am absolutely flummoxed at this point, especially because most deaths initially seemed explainable, but in totality I’m nearly certain there’s gotta be something going on I’m just not catching onto as a new saltwater hobbyist. Welcoming any and all theories. Also happy to provide more info, but to get you going:

• 38 gallons WLR. I’ve also got various CUC and corals, a majority of whom seem to be doing great.
• Parameters have been fairly steady: salinity averaging 1.023 to 1.025, Ca 400-440, KH 8-10, PO <<0.25 (API test kit, so imprecise, but appears just detectable), NO 0-10, nitrites and ammonia always 0.
• First death was a fire fish, really kinda no clue what happened, he just up and disappeared a few days after I added a handful of newbies. I’d had him a little less than two weeks.
• Second was a royal gramma. He had disappeared for a few days a week after getting him, I think because he was scared of the protein skimmer? He reappeared when I fixed the skimmer, but his fins were all torn to hell. Seemed to recover insofar as swimming around and eating, then died about a week after initial disappearance. Attributed to stress and subsequent fin rot.
• Two clowns then died within days of each other, which had followed an ATO failure the night after the royal gramma died that flushed my tank with freshwater and dropped salinity from 1.024 to 1.018. Fixed with small repeated water changes over the next few days, but they were both dead by the end of the week anyway, had them for less than two weeks in total.
• Weeks later, new royal gramma and red spotted blenny both died overnight; I’d had the former about 1.5 weeks, the latter only a few days. This followed a tank clean where I accidentally knocked around old, deep sand, so I attributed this to hydrogen sulfide poisoning. Oxygen testing really low around this point, too. Despite water changes and bringing in temporary extra pump to improve aeration, citron goby (brought in w/ royal gramma) struggled for a few extra days before dying as well.
• Six days ago, brought in new citron goby and two new clowns. All levels, including oxygen, within normal limits. No changes in behavior before they started dropping one by one overnight: the goby on Wednesday, the first clown yesterday, and the last today. Technically the last is still kicking, but the poor girl is struggling to breathe and can’t swim on her own, so obviously I’m not optimistic.

My controlling theory has been aeration issues, because the deaths have been occurring so quickly without any real warning signs. But I even added a third power head yesterday to eliminate a dead spot behind some rock work, while my last clown was still acting totally normal, swimming and eating and everything. Checked on her repeatedly until midnight with no changes, and then found her almost dead first thing this morning. She’s currently resting in a breeder box to keep her away from CUC.

Tl;dr, I can’t keep a fish alive for more than two weeks, and I have no idea why. Help?

 

[Johnd651]

Sorry, not an answer, but more questions to think about.

All from the same fish store?

Your salinity does seem to jump? Why? Are you mixing saltwater?

What's in your CUC? Something attacking the fish?

Are you running a DSB?

 

[kaleburn]

Sorry, not an answer, but more questions to think about.

All from the same fish store?

Your salinity does seem to jump? Why? Are you mixing saltwater?

What's in your CUC? Something attacking the fish?

Are you running a DSB?

• Yes indeed, all from the same LFS.
• Salinity doesn’t typically jump, just with that one ATO failure. Otherwise it’s pretty steady at 1.024, give or take 0.001 between evaporation and top offs. I don’t mix, I buy from the LFS.
• CUC is snails and hermit crabs. The hermit crabs are nasty lil buggers and attack each other and sometimes the snails, but they don’t go after the fish (nor can they usually reach them thankfully, lol).
• Sort of DSB, it’s like three inches. I suck the detritus off the top and comb it a little bit at a time about once a week to try to minimize anaerobic-related issues, though.

 

[ChrisfromBrick]

yea what someone said about swinging salinity. I'd say its probably not the cause but 23-25 might cause some stress if it is back and forth quickly? I'm honestly not so sure that is the case. Its definitely the case when your ATO failed and you had that giant swing.

More importantly, the fish store. Were these fish quarantined by you or 30 day quarantine by the fish store with copper and other meds? I don't do my own quarantine because I do want to so I buy my fish from TSM aquatics that wont sell them until they are treated for a month.

How do you know your O2? How are you measuring that?

You seem to have done your homework really well. I'm thinking fish store and if you aren't quarantining.

 

[kaleburn]

yea what someone said about swinging salinity. I'd say its probably not the cause but 23-25 might cause some stress if it is back and forth quickly? I'm honestly not so sure that is the case. Its definitely the case when your ATO failed and you had that giant swing.

More importantly, the fish store. Were these fish quarantined by you or 30 day quarantine by the fish store with copper and other meds? I don't do my own quarantine because I do want to so I buy my fish from TSM aquatics that wont sell them until they are treated for a month.

How do you know your O2? How are you measuring that?

You seem to have done your homework really well. I'm thinking fish store and if you aren't quarantining.

I’m not QT-ing, actually, most of the time I was bringing fish into an empty tank, and the other times I’d been observing them at the LFS for a while and was reasonably confident they were healthy. I do know for a fact that my LFS doesn’t QT though, they don’t have the space for it. Is it possible it’s just bad stock? I’d be surprised tbh, my freshwater buys from them have always proven hardy, but I’m so new to reefs idk if it’s like comparing apples to oranges.

For O2 testing I’ve just got a salifert kit with color-matching, it’s imprecise but at least consistent insofar as looking really pale after the suspected hydrogen sulfide bloom or looking darker since I’ve added the extra powerhead.

 

[Sophie"s mom]

Do you have live rock in the tank? If so, is there a possibility that you also have a mantis shrimp?

 

[bubbgee]

Since you dont QT, it could be a disease that is lingering in your tank. Look up fallow tank procedures.

 

[Malum Argenteum]

How do you acclimate the fish, exactly?

Personally, I would mix my own SW from RO water I made myself. I worked in an LFS that sold RO and SW, and that's part of my reasoning here.

I would also buy the next fish from a different source, just to rule out that variable.

A full tank photo might help.

 

[W31Olds]

Your 3" Sand Bed seems risky as that's pretty deep. I would check your ammonia levels as they can spike. The O2 level may be a problem but I would tend to believe you need the Fish Medics for a disease diagnosis. Not likely your ATO Failure or your Skimmer are causing your problems. If you last fish dies, I would remove and replace the Sand with a 1-1.5" bed, reseed the Tank, and go Fallow.

 

[Euphyllia97]

Hi! Sounds like you are dealing with a swiss cheese model here. The tank is 3 months old and a lot of stock has been introduced and died in a 38 gallon. From what I read there might be a combination of problems.

- Acclimation stress weakening the fish immunity causing them to be more prone to disease.

- No QT so diseases and parasites might have been introduced causing more stress.

- Unstable parameters in salinity and possible unnoticed ammonia spikes.

- Due to the amount of deaths and the age of the tank, you might have had a bacterial bloom that dropped your O2 levels causing the other fish to suffocate ( chain reaction, did you note any whitish/milky looking water at some point?)

- Torn fins, might be due to aggression but in this case I wouldn’t completely rule out bacterial issues /fin rot.

Did I assume correctly that the tank is empty now? If so, I would suggest you to run your tank at 81F for 60 days without any fish to get rid of any parasites. In the meantime ghost feed the tank so it strengthens its nitrogen cycle. In the meantime you can set up a small quarantine tank as it really is not sufficient to watch the fish a couple of minutes/hours to assess them healthy.

Treat your new fish in the QT with 30 days of copper, and 2 rounds of Praziquantel. You will be done with the process around the time your tank is safe for use again :)

 

[Dom]

I’m really sorry you’re dealing with this. Losing fish repeatedly is awful, especially when corals and inverts seem fine. But the pattern in your timeline actually points to a small number of very likely causes, and none of them suggest carelessness. They’re things nearly every new reefer gets blindsided by.

The fact that your fish keep dying suddenly, overnight, and without visible symptoms almost always indicates a systemic issue rather than coincidence. When deaths are quick and seemingly random while corals remain unaffected, the most common culprits are chronic low dissolved oxygen, toxins released from disturbed sand or rock, stray electrical issues, or environmental contaminants from outside the tank. Out of these, oxygen instability fits your situation most closely.

Your tank has been hit with several events that are known to cause steep oxygen crashes.

If this were my tank, I would immediately force strong surface agitation by aiming a power heads upward so the entire surface shimmers. I would run a protein skimmer (if you don't already have one) wet and with maximum air intake.

For now, I would hold off on adding any new fish until you see stability for a while.

The good news is that nothing here suggests you can’t turn this around. Once the underlying oxygen or toxicity issue is corrected, the tank should behave normally again.

Please post a full-tank shot because the image may reveal what’s going on.

 

[kaleburn]

Thank you all so much for the help!! Responding to a few recurring questions here:

• Pic of tank below, alongside quick video in case that’s any more informative.
• Yes live rock, no evidence of shrimpies or other secretive fellows that might be going on overnight murder sprees (or at least no evidence yet).
• I just acclimated each new fish buddy for temperature, floated the bags at the top of the tank for 30 minutes, then transferred into net to transfer into tank to avoid cross contamination from the LFS water.
• I did observe cloudy water, but only once right after the suspected hydrogen sulfide bloom. It resolved a few days later. Beyond microbubbles, the water itself has stayed pretty clear otherwise, though the glass has seen ebbs and flows of algae and other ilk.

I think that’s it, but lemme know if I missed anything or if this raises more questions. My last lil clown indeed passed in the last few hours, so fallow it is

 

[56longroof]

Your 3" Sand Bed seems risky as that's pretty deep. I would check your ammonia levels as they can spike. The O2 level may be a problem but I would tend to believe you need the Fish Medics for a disease diagnosis. Not likely your ATO Failure or your Skimmer are causing your problems. If you last fish dies, I would remove and replace the Sand with a 1-1.5" bed, reseed the Tank, and go Fallow.

Not true at all about the sand. If that's the case my 6" deep sand would kill everything. The sand did not kill the fish and the hydrogen sulphide theory is a load of BS in my opinion. Its one of those stories that keeps getting told with no actual evidence. Its more likely the places you are getting them and the tank only being 3 months old. Your adding alot of fish rather quickly. Slow down add 1 or 2 a month.

 

[Dom]

Thank you all so much for the help!! Responding to a few recurring questions here:

• Pic of tank below, alongside quick video in case that’s any more informative.
• Yes live rock, no evidence of shrimpies or other secretive fellows that might be going on overnight murder sprees (or at least no evidence yet).
• I just acclimated each new fish buddy for temperature, floated the bags at the top of the tank for 30 minutes, then transferred into net to transfer into tank to avoid cross contamination from the LFS water.
• I did observe cloudy water, but only once right after the suspected hydrogen sulfide bloom. It resolved a few days later. Beyond microbubbles, the water itself has stayed pretty clear otherwise, though the glass has seen ebbs and flows of algae and other ilk.

I think that’s it, but lemme know if I missed anything or if this raises more questions. My last lil clown indeed passed in the last few hours, so fallow it is

One thing I would comment on is the placement of the power heads.

Tank flow should be chaotic. You achieve this by pointing your power heads at each other.

The positioning of the power heads has water flowing in a circular motion, much like stirring a pot.

 

[petcellar]

Hi! Sounds like you are dealing with a swiss cheese model here. The tank is 3 months old and a lot of stock has been introduced and died in a 38 gallon. From what I read there might be a combination of problems.

- Acclimation stress weakening the fish immunity causing them to be more prone to disease.

- No QT so diseases and parasites might have been introduced causing more stress.

- Unstable parameters in salinity and possible unnoticed ammonia spikes.

- Due to the amount of deaths and the age of the tank, you might have had a bacterial bloom that dropped your O2 levels causing the other fish to suffocate ( chain reaction, did you note any whitish/milky looking water at some point?)

- Torn fins, might be due to aggression but in this case I wouldn’t completely rule out bacterial issues /fin rot.

Did I assume correctly that the tank is empty now? If so, I would suggest you to run your tank at 81F for 60 days without any fish to get rid of any parasites. In the meantime ghost feed the tank so it strengthens its nitrogen cycle. In the meantime you can set up a small quarantine tank as it really is not sufficient to watch the fish a couple of minutes/hours to assess them healthy.

Treat your new fish in the QT with 30 days of copper, and 2 rounds of Praziquantel. You will be done with the process around the time your tank is safe for use again :)

 

[W31Olds]

Not true at all about the sand. If that's the case my 6" deep sand would kill everything. The sand did not kill the fish and the hydrogen sulphide theory is a load of BS in my opinion. Its one of those stories that keeps getting told with no actual evidence. Its more likely the places you are getting them and the tank only being 3 months old. Your adding alot of fish rather quickly. Slow down add 1 or 2 a month.

I did not say the DSB killed the OP's fish. Just that for a new hobbyist, it can be problematic. I did say that that a parasite is the most likely cause and that's why I recommended to Fallow the Tank. For the OP, we need more background on where you got you Fish and were they QT'd.

 

[Malum Argenteum]

I just acclimated each new fish buddy for temperature, floated the bags at the top of the tank for 30 minutes, then transferred into net to transfer into tank to avoid cross contamination from the LFS water.

Unless you matched salinity/SG, this might be a major contributing factor.

https://www.reef2reef.com/ams/acclimation-methods.903/
Pretty tough to match water conditions without a QT tank, so that's something long term to think about as well (aside from the usefulness of a QT tank for preventing fish from bringing in disease to the DT).

 

[winzig]

to much to soon it seems to me.

 

[StradicCi4]

From the way it reads, you've made bigger mistakes that have ended up in the death of your fish. The ATO failure, the oxygen depletion etc.

Stay consistent and let it stay fallow for a couple months to rule out any parasites.

 

[scottmckinney67]

The best advice I can give is slow down. Add 1 hardy fish and wait. Also, do a section at time when cleaning the sand. Hang in there.