Tank having a huge crash

Liam_1 · Aug 31, 2025

Hey everyone, i need some help

a week ago i lost 2 of my chromises. I thought it was just a weird case and shook it off cause values seemed fine and corpses were gone so i thought my shrimps were taking care of it, and i replaced them with an algae eating blenny.

So it leads me to Last thursday. My friend comes over and i let him sleep in my room. The guy turned on the ac on 18 celsius for god knows how long and i only discovered it when i woke him up, i immediately closed the ac but my heater didnt stand a change against it in a closed room. it was already on 22 celsius, but the fish and corals survived and opened up

then yesterday my ac decided to shut down and temperature spiked to 26 celsius while i was out for the weekend. came back only today to see all of my fish died (2 clownfish and 1 wrasse) but the blenny, milky waters, closed up corals and - no bodies found. AT ALL. i assume my shrimps are fast eaters and my fish were small.

Anyhow i measured 1ppm phosphate, 3ppm nitrite, 25ppm nitrate and ammonia is <0.15ppm
i now changed water and adsorbers and put double the dosage in the tank to quick things up.

So my question is - what are the following steps? what do i do in order for the corals and blenny to survive?
and what on earth made it happen? i do know that temperature spikes are awful, but 22-26 celsius is not a deadly range so why did they die? is it just the range was big do that made them die? or maybe they had the white dots disease and i didnt notice?

smitten with ocean life · Aug 31, 2025

#reefsquad

Talisker · Aug 31, 2025

I'm too newb to answer the survival question. Do you know for sure your tank temperature peaked at 26c during the ac outage. If that happened to me in my experience so far my tank temperature would go way higher than that. But I'm east coast USA and my internal house temp would soar to 30+ and my tank would go with it

Mr. Mojo Rising · Aug 31, 2025

It’s a small temp change it wouldn’t have any significant impact. This is not why the fish died. But don’t you have a heater in your system?

3 nitrite means you had an ammonia spike, so what happened? Did a fish die, did you over feed , are you not changing water regularly? Something happened to the water.

Need more info on your system- how big is the tank, how many fish, how is the tank oxygenated, a picture would really help….. need more info and pictures please

gbroadbridge · Aug 31, 2025

smitten with ocean life said:
#reefsquad

I don't believe there is a reefsquad anymore, apart from a few old badges.

smitten with ocean life · Sep 1, 2025

no theres a reef squad! @Rocks reef , @Fish Fan ? who all is it?

Liam_1 · Sep 1, 2025

Talisker said:
I'm too newb to answer the survival question. Do you know for sure your tank temperature peaked at 26c during the ac outage. If that happened to me in my experience so far my tank temperature would go way higher than that. But I'm east coast USA and my internal house temp would soar to 30+ and my tank would go with it

The good thing is i live in a basement and i still have a tiny vemtilator in my tank for emergencies like this. So my room was still a bit colder than the actual temp outside

Mr. Mojo Rising said:
It’s a small temp change it wouldn’t have any significant impact. This is not why the fish died. But don’t you have a heater in your system?

3 nitrite means you had an ammonia spike, so what happened? Did a fish die, did you over feed , are you not changing water regularly? Something happened to the water.

Need more info on your system- how big is the tank, how many fish, how is the tank oxygenated, a picture would really help….. need more info and pictures please

I do have a heater but its a small one and the ac on full intense is winning in this fight lol.

I already wrote in the first message that all my fish died. Thats the reason for the spike in nitrite. I only have a blenny and a goby left alive (and the shellfish)

My tank is 11 gallons, its oxygenated by wet skimming + return pump outlet is directed upwards + wavemaker. My pH is steady on 8.15 all the time.

Im sending the last pic i took of tha tank

Mr. Mojo Rising · Sep 1, 2025

It sounds like you had 5 or 6 fish in that 11 gallon, sorry, but that was doomed from the beginning. You can only fit one, maybe two small fish in that size tank, thats it. You way overstocked the tank and overloaded the filter capability and ammonia started rising and killed the fish. Nothing to do with air conditioning. Sorry for your loss but please try to understand what happened and avoid overstocking.

Liam_1 · Sep 1, 2025

Mr. Mojo Rising said:
It sounds like you had 5 or 6 fish in that 11 gallon, sorry, but that was doomed from the beginning. You can only fit one, maybe two small fish in that size tank, thats it. You way overstocked the tank and overloaded the filter capability and ammonia started rising and killed the fish. Nothing to do with air conditioning. Sorry for your loss but please try to understand what happened and avoid overstocking.

Thank you for the advice, i will now know for the future to not put more than 2 fish...
Still, what do i do now to save the corals? I have like 20 of them

Mr. Mojo Rising · Sep 1, 2025

Liam_1 said:
Thank you for the advice, i will now know for the future to not put more than 2 fish...
Still, what do i do now to save the corals? I have like 20 of them

The corals don't have any bioload so you can have as many as you want. I would just do a 50% water change to clean out the tank. Good luck

Rocks reef · Sep 1, 2025

Also, the shrimp would never be able to eat a dead fish that quick. They dead chromis are still in there rotting, or they jumped out and you haven't found them.
The dead fish is causing a bacteria bloom, hence the 'milky water'.
I'd start by finding the dead fish.
I'd continue water changes.
I would not add as many fish to a 11 gallon tank. As mentioned above by @Mr. Mojo Rising . Keeping a few select SMALL fish in there is fine.

Rocks reef · Sep 1, 2025

smitten with ocean life said:
no theres a reef squad! @Rocks reef , @Fish Fan ? who all is it?

We are quite alive and trying to keep up on threads. There are a few of us Jill and Rev will be making a post shortly to introduce us to R2R.

Rocks reef · Sep 1, 2025

gbroadbridge said:
I don't believe there is a reefsquad anymore, apart from a few old badges.

It is alive and well sir. Rev will be making a post shortly to introduce the members.

Bruttall · Sep 1, 2025

26degree Celsius is 78 degree F. Coral thrives at 74 to 80 F. It wasn't the temperature that killed your fish. Here is a Screen Cap from my Apex temp readout. 300g Mixed Reef display.

From the Test you posted I'd guess that dead fish caused a pretty substantial Ammonia Spike, and that most likely is what killed the rest of your fish. Sorry that happened.

Liam_1 · Sep 3, 2025

Guys i dont know what to do!
I changed water every day, and a lot (50 percent) and my phosphate has gone up to 3ppm! Thats huge!
What do i do? I feel helpless and im afraid to lose all my corals

js-3Design · Sep 3, 2025

well, your heater is too small then... In the winter my livingroom is 14-15C. I run a 200w titanium heater on a 200L tank and run the tank stable at 25c

Liam_1 said:
Guys i dont know what to do!
I changed water every day, and a lot (50 percent) and my phosphate has gone up to 3ppm! Thats huge!
What do i do? I feel helpless and im afraid to lose all my corals

the first thing you do is getting rid of some of your fish, take them back to the store.

there is too much organic material on the rocks and sand in corners and so on, that gives of to much phosphates.

your overstocking experiment was never going to work.

Liam_1 · Sep 3, 2025

js-3Design said:
well, your heater is too small then... In the winter my livingroom is 14-15C. I run a 200w titanium heater on a 200L tank and run the tank stable at 25c

the first thing you do is getting rid of some of your fish, take them back to the store.

there is too much organic material on the rocks and sand in corners and so on, that gives of to much phosphates.

your overstocking experiment was never going to work.

ok so my only remaining fish i will return, but i meant what i could do else? Like water changes or maybe phosphate adsorbers etc?

And, there is no reason to tell me "your overstocking experiment was never going to work" - thats my first tank. I got in the hobby only a few months ago. I didnt know this.

Lasse · Sep 3, 2025

It is the remains of your dead fish that are mineralized by bacteria that cause your nutrient explosion. It will continue as long as there is leftover from the dead fish.

Of course, with water changes, GFO and other tricks you can improve the situation over time but now I will give a piece of advice I very rarely give. Start over - and here is how I would do it.

Prepare a bucket of new saltwater and move your corals and fish there. Use an air pump with an air stone or a circulation pump in the bucket. Darken the bucket while you prepare the aquarium

Remove all the water from the aquarium but save half a gallon or a little less (future nutrition for your corals). Remove rocks that do not have any corals and rinse them off. Remove the sand - wash all the sand thoroughly with tap water except for half to 1 kilo which you just rinse off a little with new saltwater (your bacteria culture for a fresh start). Place your rocks out. Fill with the tap water washed sand and then spread the sand you just washed gently with saltwater in a l layer over the other sand. Carefully fill with new saltwater - be careful not to disturb your sand bed. Finally, add the old saltwater you saved. Turn on all pumps and other equipment. Move your corals and fish over there.

Feed very sparsely in the beginning - feel free to follow the advice here

A word about overstocking.

In my world the word overstocking seldom exist but overfeeding do! With five small fishes in a 11 G there is no automatically overfeeding taking place. If you feed sparsely with frozen food like adult artemia and others - there is no problem. However - your fish will grow and 5 adult fishes if these species you have may demand to much food on a daily basis and give to little space for them - even if they use different part of your aquarium. But using only frozen or fresh food - they will grow slowly as they do in nature.

In my 80 G I have for the moment around 40 fishes - including a tang (of the smallest species), a copperband (been in the aquarium for more than 6 years) and an adult male of blue star leopard wrasse (been in the aquarium for more than 8 years) Right done - 5 fishes in a 11 G is no catastrophe - wrong done a fry of any fishes is way to much.

Sincerely Lasse

Liam_1 · Sep 3, 2025

Lasse said:
It is the remains of your dead fish that are mineralized by bacteria that cause your nutrient explosion. It will continue as long as there is leftover from the dead fish.

Of course, with water changes, GFO and other tricks you can improve the situation over time but now I will give a piece of advice I very rarely give. Start over - and here is how I would do it.

Prepare a bucket of new saltwater and move your corals and fish there. Use an air pump with an air stone or a circulation pump in the bucket. Darken the bucket while you prepare the aquarium

Remove all the water from the aquarium but save half a gallon or a little less (future nutrition for your corals). Remove rocks that do not have any corals and rinse them off. Remove the sand - wash all the sand thoroughly with tap water except for half to 1 kilo which you just rinse off a little with new saltwater (your bacteria culture for a fresh start). Place your rocks out. Fill with the tap water washed sand and then spread the sand you just washed gently with saltwater in a l layer over the other sand. Carefully fill with new saltwater - be careful not to disturb your sand bed. Finally, add the old saltwater you saved. Turn on all pumps and other equipment. Move your corals and fish over there.

Feed very sparsely in the beginning - feel free to follow the advice here

A word about overstocking.

In my world the word overstocking seldom exist but overfeeding do! With five small fishes in a 11 G there is no automatically overfeeding taking place. If you feed sparsely with frozen food like adult artemia and others - there is no problem. However - your fish will grow and 5 adult fishes if these species you have may demand to much food on a daily basis and give to little space for them - even if they use different part of your aquarium. But using only frozen or fresh food - they will grow slowly as they do in nature.

In my 80 G I have for the moment around 40 fishes - including a tang (of the smallest species), a copperband (been in the aquarium for more than 6 years) and an adult male of blue star leopard wrasse (been in the aquarium for more than 8 years) Right done - 5 fishes in a 11 G is no catastrophe - wrong done a fry of any fishes is way to much.

Sincerely Lasse