shark tank crash

[FishyMel]

When I woke up this morning I did my usual check out all my fish and make sure they're ok, but when I went to my shark tank I found the little girl upside down on her back barely breathing. I took her out of the tank with my hand thinking that what ever it was, it can't infect the fish in my 200 if I add no water (shark and fish parasites don't intermingle), and I put her in the refugium of the 200. Currently she is breathing fine, rightside up, and moving a little less than usual but that could just be acclimation shock, we'll just currently hope for the best. But anyway In the tank with her the mushrooms all look horrible and are approaching death and weirdest of all, the Cyano bacteria died. Yesterday the tank was fine and she ate well but the then today I wake up to a half dead shark. I tested parameters
Nitrates 20
nitrites 0
ammonia 0
ph 8.4 (at noon)
salinity 1.022

What could have happened I've been adding Iodide and not doing water changes to take out the iodide but the bottle says it naturally goes away and contains nothing harmful. One theory I have is that I keep my tank half stocked with caulerpa and the shark hangs out in the center. I do this to keep nitrates low since the aquarium isnt reef ready, I can't have a fuge on it. And my theory is that since I haven't cut the caulerpa back, it was growing exponentially to the point where one night it just sucked too much oxygen than the shark to handle, you'd still think though that I'd be noticing sluggish behavior in the morning the weeks before. I still don’t know what happened, any explanations?

[TheSaltwaterGuy]

You haven't been adding any copper-based medications to the tank have you? If not, its definitely the nitrates. Try to lower them ASAP.

Tell me something. Is the shark's belly reddish colored? If so, it was bothered by the nitrates. What I would do is keep the shark in the fuge for now and get those trates lowered and introduce her back to the tank, then go from there.

[FishyMel]

From what I read anything under 30 for nitrates is fine, her belly is fine too. Nitrates also don't describe the death of the cyano algae and shrooms and how instant the whole crash was. No, I did not add any copper merdications, that would be moronic with a shark and inverts. The whole situation came very suddenly and strange. My only logical theory is the plants sucking oxygen which also would drop ph creating a double whammy.

[TheSaltwaterGuy]

Where did you read that? My shark reacts to any thing over 10ppm. And not in a good way. I've been through the whole nitrate problem, as well, and as you know its not fun if you have a shark.

My suggestion would be to keep fighting down those nitrates and cut back some of those plants, just in case that was what happened.

[jcjstl]

Did the caulerpa go sexual? That would pretty much explain almost the whole tank dying off.

[billsreef]

The nitrates, while a tad on the high side for sharks keeping, are not high enough to cause the problems you are describing. Quite likely a result of some of that caulerpa going sexual or just having released a critical level of toxins that have accumulated over time. Another possibility is accumulation of other elements, especially metals if you use untreated tap water for top off. The lack of water changes often leads to such accumulations. I would consider water changes just as important, if not more so, to a shark tank as a reef tank. Best way to be sure your shark is getting enough iodine is to feed it foods heavy in iodine such as shellfish, adding iodide to the water is very inefficient and even questionable in reef tanks.

[TheSaltwaterGuy]

Got any pics of the shark?

[FishyMel]

The caulerpa going sexual is I think now the most probable cause of the crash. Here is a picture of her mouth, the only pic I have of her on my computer. It is a rather nice looking mouth though I must say, I also have a picture of her still 2 cm long in her egg but I think that was too long ago for what you want to see

[FishyMel]

[krj-1168]

Yeah - Nitrates of 20ppm - is too high for shark. It absolutely needs to be below 10 ppm, - 0ppm is best, if possible.