Urgent help needed All fish dead

11 Sep 2009
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Yantai, China
Please help. I will give some background on my tank. Please give advice.

Tank initial set up: 650 L
DT: started 1,5 years ago with dead rock, used zeo products (bak, food, start). Live rock is very porous and has cyvled well.
Used jebao rw15 x2 for flow. C2c back drop.

Sump: filter sock, bubble magus 8 skimmer, second chamber has chaeto and marinepure blocks. Last chamber has carx reactor and return pump. I am semi OCD so I keep my sump very clean.

I’ve always had some issue with algae, about a month ago I found out that my return pump is completely underrated so I switched it from the jebao 7000 to a jebao dcp 15000 and run it at 75 watts. With my head pressure this give me 6000L returned to the dt. I’ve also change the flow pumps to the 3rd gen maxspect gyre pumps.

Since changing these the algae has quickly started to die off, so 2 weekends ago I started pulling it. My skimmer went crazy for about 2 days. The rocks still had quite a bit algae on it so 2 days ago I took a new tooth brush and brushed it of, thats how quickly the algae was dying off.

When doing that it made a big cloud of dust which settled rather quickly. Again, the skimmer went crazy.

30 minutes later I noticed my foxface acting lethargic. I tested the ammonia and it was 0.15 on the salifert test. 10 minutes later all my fish was dead... tested ammonia again and it had shot up to 0.50 in 10 minutes. Also, the pH went from 8,2 to 7,97 in about 4 hours time.

The shrimps, snails and corals seemed fine. The day after I tested ammonia again and it is back at 0.15, tested it just now again and it’s undetectable.

So, what caused this? What do I need to look out for? How to prevent this from happening? What am I missing here?
10 Oct 2012
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Hi from what i read here the first thing that comes to mind is the rate at which the algae died off. Dying algae will convert into ammonia which at the time you brushed it off obviously released all the trapped pockets of ammonia build up. The adding of more oxygen (bigger turnover ect) would also be a concern as it most probably all happened in a short span of time. In my opinion the fish dying indicate to me that it was a sudden ammonia release.


11 Aug 2008
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Too much die-off in very short timespan.

Sounds like the amount of algae brushed off is a lot. Should have rather remove the rock and scrubbed it in a bucket of old tank water. Same time you do a rather big water change on your system.

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