Fish Dying Biocube

[BC1906]

I have had a biocube 29 up and running for about 2 months now. I had a pair of ocellaris clownfish in there for a month. I recently ordered a RW4 Powerhead and added it to the tank to help with the circulation for my corals. The very next day one of my clownfish had died. My guess would be is that the powerhead stirred up some of the sand and it released toxins into the water that caused the fish to die. I did a water change and everything seemed fine but now my other clownfish has died a couple of days later and I can't figure out what is going on. I cycled the tank for about a month with 15-20lbs LR and about 20lbs of LS. All of my parameters look to where they need to be. Ammonia and nitrites are at 0, PH is at 8.2, salinity is 1.025, Phosphate 0, nitrates are about .5 and my temp is around 79. My Alk is also looking good. I am currently using a self made media rack out of eggcrate with filter floss and chemipure elite.

Does anyone have any suggestions on what could be causing the fish loss? I have a star polyp, torch coral, frogspawn, and a zoa that all seem to be doing fine. My CUC consists of 1 peppermint shrimp, 4 hermit crabs and 5 nassarius snails which now are the only things in the tank.

Any suggestions would be great. I am obviously going to hold off getting anymore fish for right now until I can figure out what is going on but I dont know where to start since my parameters seem fine.

[Mrramsey]

What are your ammonia and nitrite levels? Should be zero.

If they are present the tank is not cycled or a mini cycle has spiked.

[BC1906]

Ammonia and nitrites are at 0, PH is at 8.2, salinity is 1.025, Phosphate 0, nitrates are about .5 and my temp is around 79.

[Mrramsey]

Any stirred up sand would have kicked up a mini cycle but since the ammonia and nitrite are zero I doubt that was it. Any chance chlorinated water was added during the top off?

[BC1906]

I do not believe there was any chlorine as i use premixed reef crystals that I get at my local shop. I have not had to top of the tank with freshwater since it hasn't really been evaporating and my salinity is where it needs to be. I will sometimes put a couple of drops of Prime in there just to make sure there is no chlorine but I add a fraction of what it calls for on the bottle due to the sulfates it adds.

[OrQidz]

So the fish died right after the powerhead was added? Hmm. I wonder about a couple of things:

1) new piece of equipment and fish dying, I wonder about stray voltage or something on the equipment itself. I doubt it could be copper leaching since your inverts are ok. Any oily film on the water surface at all?

2) water quality issues is a common culprit but your corals are doing ok...and your parameters are doing ok. I find it interesting you have hardly, if any evaporation? I run my BC open top so I guess I am just used to topping off a lot. What are you adding the prime to then? If you are using prime for tap water, you need to use the full dose. How often are your water changes?

[BC1906]

Yeah I am running mine with the lid on so not much evaporates between my water changes. I will sometimes at the prime to the premix I get but I don't often do it. I always use the full amount of it if I am using straight tap water. Right now I do about 10% water change once a week and 20-30% once a month. I don't see any type of film and my inverts all seem to be doing fine.