My fish are dying, help!

[sg390303]

I have 2 saltwater fish tanks that have been set up and fine for over a year, I did a water change two days ago and when I woke up half of my fish were dead.

75 gallon
tomato clownfish
yellowtail damsel
sailfin tang - at the bottom breathing really hard, looks almost like it's having a seizure
hawkfish - dead
coral banded shrimp - dead
bicolor pseudochromis - dead
electric flame scallop
brittle star - all of his legs are falling off, but still alive
pencil sea urchin
hermit crabs

Also, a few weeks ago I got some new live rock, which apparently came with some "nuissance anenome." Could that kill everything?

55 gallon tank
seahorse
sand sifting star
pink/purple sea cucumber
scooter blenny -dead
hermit crabs

Okay, here's the story: My fish were all fine, but my nitrates were high, so I did a water change (25-30%) on both tanks. The water change occurred during the evening, and when I woke up in the morning my shrimp, hawkfish, and pseudochromis were all dead. My tang was at the bottom of the tank, breathing really fast and looking like she was having a seizure. My damsel was pale colored and my clownfish was swimming at the top of the tank and hovering there. I quickly checked on my 55 gal and it was fine, everyone was still alive. I figured my best bet was to put my tang into the 55 gal until I figured out what was wrong. So, I moved her and went back to the 75 gal. I realized that my aerator had gotten unplugged and so I fixed that. The tang was starting to look a little better in the other tank--no more seizure looking activity, but she still wasn't swimming and she was still breathing hard. I fed the other fish in that tank and hoped she'd look better tomorrow.

The next day, I got my water checked and they were both fine, but they were unable to check my salinity. I had always used a floating hydrometer for water changes, so I decided to get a stand alone one at the store to check. The salinity in my 75 gal was 1.028. I got it gradually lowered over the course of the day to 1.0245. The salinity in my 55 gal was 1.024. My tang still wasn't doing so well, so I figured I'd leave her in the 55 gal.

Today I woke up to find my tang still at the bottom breathing hard at the bottom of my 55 gal and now my blenny was dead. My damsel still looks pale and my clownfish is still swimming up at the top of the tank.

What should I do? What's wrong with my tanks? Should I keep changing my salinity? Is there something else I should check?

And on a side note, I recently have had a lot of long stringy hair algae growing in my 55 gal.

Please help!

[sg390303]

Oh, and here is what the results were when I had my water checked:

75 gal
Ammonia- 0
Nitrate- 200
Nitrite- 0
Alkalinity buffering capacity- 240
pH- 8.0

55 gal
ammonia- 0
nitrate- 40
nitrite- 0
alkalinity buffering capacity- 240
pH- 8.0

[Parrothead]

I'm gonna wait for leebca to chime in here, but I believe we need alot more info as to that nitrate reading in the 75 at 200, 200 what???????????? ppm??????????, I have personally never seen a test kit that can test that high if it's ppm,

[sg390303]

Yes, ppm

[sg390303]

I was gone for a few weeks and I had someone else feeding my tanks. I think they were just overfed.

[sg390303]

Update: I just lowered my salinity in my 55 gal from 1.024 to 1.023 and my tang is actually swimming around and looking much happier. But now that she's swimming around I have noticed that she's got big areas where her scales have been rubbed off due to her just laying at the bottom rubbing up against live rock for a couple of days. She's looking pretty beat-up physically. Is there anything I can do to help with that?

[leebca]

The tank was most likely poisoned. All sorts of possibilities here: the new live rock was not totally cured; food rotting; bad water change; etc. Although overfeeding could be the, or part of the, problem, there is also a possibility somebody put something into the tank that shouldn't have gone in there (including the live rock -- see above).

Your best action is to perform a daily huge water change, for the next week. I'm talking over 80%. But you need to follow these guidelines to make this kind of water change: How to Make a Successful Water Change

Having written the above and reviewing your posts, there is a good chance that the water change you performed was not done properly and may be complicated by waiting too long. Maybe the source water was poisoned/bad? The high nitrates indicates that the water changes have not been kept up properly or there is a large amount of biological filter activity (like from over feeding, or live rock die-off). For a tank that hasn't had a water change for a long time, fish tend to get used to water that is off-quality. When a water change occurs, they can go into shock or die. It depends alot on whether or not you checked the pH, temp, salinity, alk, calcium, and magnesium before you did the water change, in order to match them with the new water. It is often a hobbyist error to think that they can correct bad water by doing a water change. A proper water change doesn't alter the water chemistries (like pH) which the fish are very sensitive to. A water change is meant to remove wastes that adversely affect the system, and to put back in some micro elements and constituents used by the inhabitants.

The alkalinity reading is of little use without also having a calcium and magnesium reading. These three must be kept in balance, not just each in their individual ranges. This post explains the balance: What is Water Quality.

Regarding the marine life forms: I would not keep any hermit crabs and the Tang should be in a longer aquarium. But the inhabitants should be okay, even with the hitchhiking anemone.

This is about all that I can say at this point in time, without more information.