Tank not happy - diagnosis?

[jjirsa78]

I have a relatively fully (over) stocked 24G Nanocube, with ~7-8 soft corals / LPS, 5 fish (royal gramma, purple firefish, 2 green chromis, false perc), and various shrimps/crabs/snails.

Woke up this morning and found the basslet breathing hard and laying sideways on the substrate in a narrow point between the rocks and back wall (an area of moderate/strong current flow), and the corals closed. None of the other fish came out for feeding (definitely unusual for these guys), but they were definitely swimming upright in/around the rockwork. Temperature was OK, and being incredibly late for work already, I didn't take the time to test params...

I did a 3G water change (10%'ish), added in the surface skimmer attachment to help in oxygenating the tank (wild guess based on the basslet's breathing), and added fresh carbon and the Kent ammonia detox (another wild guess based on past experiences). Within about 20 minutes, things were back to normal (everyone out and swimming, eating, corals opening).

Now - I know I should have tested everything ahead of time to understand what the real problem was, but does anyone have any guesses?

 

[bromion]

Maybe something died in the tank and caused an ammonia spike? Anything substantial missing?

 

[jjirsa78]

All fish, shrimp, and turbo snails accounted for... Didn't count any of the smaller items (hermits, nassarius, stomatellas). A 3/8" mushroom got smashed between some rocks and melted away over the weekend, but that seems pretty small. Death would have been my first guess, since in such a small tank, it can cause quite a spike, but I'm not seeing anything...

 

[NicoleC]

pH this morning? pH now? Normal ph?

An overnight O2 drop does seem to be the best guess in an overstocked tank and with those symptoms. I would begin tracking overnight pH drops, and until you can do that, keep the skimmer running at night with a nearby window cracked.

 

[jjirsa78]

Normal pH in the 8.3 range. Didn't get a chance to check pH, will start graphing it 3-4 points a day starting tonight ...

Guessing the combination of overnight o2/pH to be the best guess so far.

 

[NicoleC]

Low pH is often a good sign of low O2, that's why I asked about pH.

 

[jjirsa78]

Assuming the pH is sufficiently high, any other thoughts? If this persists or returns, what should I be looking for?

 

[NicoleC]

Ich and/or other gill parasites is an option, as they latch on to the fish while they are sleeping.