Overnight crash - unknown cause

[Jason Scalise]

I recently had a total crash in my IM 20...and I am not entirely sure why.
Looking for possible answers as a learning point.
The question is: what was most likely the cause for the rapid crash of what seemed like a very stable and happy tank.
And given that things stabilized pretty quickly afterwards...was it possible a coral spawn that made the tank toxic?
I ask this because, as you will see below, the PO4 went from stable to off the charts and then back down again. If PO4 was chronically high due to overfeeding, etc....I would have assumed that it would take much longer to get it down for good as it would continue to leach out of the rocks.

I know crashes happen. I have more heartburn not having a good idea why this one happened.
Any thoughts would be appreciated.

Background
Mature tank (2 years), stable and great growth.
Dosing AFR and that's it.
No changes in habits, nothing new added.
here is what it look like just a few days prior.



Parameters had been stable and going a year back on Apex charts they remained at...
Alk 7.5-7.8
NO3 5.0-6.0
PO4 0.1-0.2
Ca 420-430
Mg 1300
SG 1.025
temp 78


Crash Day
I awoke to a completely cloudy tank, milky white...and RTN starting in the birdnest and all other corals like hammers, zoas and goniporas closed up and looking unhappy. They were all super happy the day/night before.

Tested parameters that morning and
Alk 8
PO4 .99 and off the Hanna chart
NO3 10
SG 1.025


Assuming it was bacterial bloom (but still was not sure why) I did several massive water changes, added an airstone, added some GFO for about 3 days and then removed it when PO4 was closer to 0.20 range.
I ended up losing most corals and snails.
The 3 fish and pistol shrimp survived and never looked stressed, to be honest.
Went from this...


To this...basically overnight.


Chalice was totally dead. In the dumpster. Was a shame because I purchased that when it was the size of a quarter.
The nutrients came back down in few days and have remained stable although I had to recalibrate AFR dosing as there was little left for consuming Alk at that point.

The zoas survived as did both euphyllia and both goniopora.
In fact the Gonis look like they did before. See video here...
I have started to add frags back to the frag rack.

Still not sure what happened. Did the parameters go from stable to unstable or were the high nutrient readings because of something introduced (spawning)?

 

[smitten with ocean life]

wow. i have no ideas for you but im really sorry!!

 

[Marco_99]

Was there any maintenance done on the tank in the prior days leading up to the incident

 

[Lavey29]

Sounds like a doser or filtration issue

 

[draj]

any candles, cleaning supplies, etc used in the home the night before?

 

[UncommonSense]

Check your equipment… an electrical fault can cause current leak into the water, and/or a significant dose of copper!

 

[Gone Reefin’]

So sorry this happened. Everything seems to point to rapid oxygen depletion, based on the very quick death. However the phosphate is a wrinkle, but I suppose the rapid death could have immediately boosted nutrients? If we assume this, then we have to find source of O2 depletion. Bacterial bloom is a possible culprit, but something would have had to change. Any new supplements recently? Do you have any macroalgae that could have gone sexual?

 

[Gone Reefin’]

Hmm just saw that your fish survived, so this would make O2 depletion a less likely cause.

 

[Uncle99]

Temp spikes or fluxes can kill invert stuff.
Broken heaters as well.

I’ve had trouble with birds net before. They grow big fast, but then quickly let go.

Very fragile frame.

 

[ptrusk]

The milky water suggests:
1) Calcium carbonate precipitation. Due to OD of alk. I don't use AFR so can't help you there. If this was the case, you would notice white dust everywhere for a while until it is redissolved. How do you dose alk?
2) Spawning event. I had a large hammer colony spawn years ago that turned the tank milky. Would explain phosphate spike. You don't mention filtration but the goo in the water could have queered the phos reading and filtration removed it. Your hammer is small so I don't know.
3) Bacterial bloom.

Do check you pH. May provide another clue.

EDIT: I just noticed you lost the stunner too. I didn't think it was possible to kill them but whatever cheesed that off was likely the cause.

 

[Jason Scalise]

Was there any maintenance done on the tank in the prior days leading up to the incident

The only thing done the day before was reducing the ball of chaeto by half as it was getting too large. Not exactly a major maintenance event.

 

[Jason Scalise]

any candles, cleaning supplies, etc used in the home the night before?

Nope. None of that.

 

[Jason Scalise]

any candles, cleaning supplies, etc used in the home the night before?

Check your equipment… an electrical fault can cause current leak into the water, and/or a significant dose of copper!

So sorry this happened. Everything seems to point to rapid oxygen depletion, based on the very quick death. However the phosphate is a wrinkle, but I suppose the rapid death could have immediately boosted nutrients? If we assume this, then we have to find source of O2 depletion. Bacterial bloom is a possible culprit, but something would have had to change. Any new supplements recently? Do you have any macroalgae that could have gone sexual?

no new supplements.
Have chaeto and have had for a year or so.

 

[Jason Scalise]

Temp spikes or fluxes can kill invert stuff.
Broken heaters as well.

I’ve had trouble with birds net before. They grow big fast, but then quickly let go.

Very fragile frame.

Agreed but given that I can look at apex readings, everything including temp was within normal limits. I test parameters about once per week or two as well.

 

[Jason Scalise]

Thanks everyone. I read through all of the suggestions and appreciate the feedback. Smaller volume tanks (like my 20g) is certainly easier to have more dramatic swings. Given everyone's suggestions, I dont think I was missing anything super obvious. Always lots to learn.