Xenia Meltdown (aka pH dropped!)

[psumba]

Ok I need someone elses opinion - this upset me all yesterday and I couldnt sleep last night:
I have had my Xenia for 2 weeks now, he has been growing new polyps and starting to divide. Saturday night I decide to change 10% (55 gal tank) of the water - first water change since I have had the coral.
I changed my 6 gals, added 6 back (used NovAqua, and Amquel, similar specific gravity), topped off with some fresh and minor amount of more saltwater - ended my specific gravity at just under 1.023
Then added Kent Marine Iodine, Liquid Calcium, Strontium
Did all the water tests: 8.2pH, 0 Nitrate, 0 Phosphate, 405 mg/L Ca
(Used 1 vile twice, of course I rinsed with freshwater inbetween, and one I realized I pulled out un-needed, and poured that water back)
Since I was under in Ca - I added 15 more drops of Liquid Ca.
Tank looks beatiful, everyone is happy.
My wife notices that the Xenia was starting to retract its polyps. I figure that it must be closing for the night - its close to lights out.
Next morning - He is melting!! and does not look so good. Observed everyone else, no one is bothered by anything. Check the Protein Skimmer it became half full over night. (Though I am still playing with it to try and get it to be full blown open, doesnt happen without it pouring pure liquid into the cup)
I check the water quality last night. Only changes are my pH is now 7.8! and my Ca is up to 510. In the begining of setting up the tank I had noticed at times it would be 7.8...but hadnt been in awhile.
last night I changed another 3 gals.
So what happened? Apparently my alkalinity is not so good and my pH crashed, but what would cause it?
BTW -tested the freshwater from the pipes 8.6pH
Background - this tank used to hold African Cichlids, would they have produced something that is still in the tank and caused this?

 

[don berry]

I would say that the ph drop is exactly the problem. Xenia's like a high ph, and obviously yours is dangerously low. Do you add any kind of buffer to keep your alkalinity and ph up? I use seachem and it works great for me. I don't know how far gone your Xenia's are, but I've been able to bring mine back when they looked really droppy one time. Try slowly raising your ph with a buffer, and hopefully they will make it.

 

[don berry]

Oh yeah, I can't give you the scientific reason why this happened, but I do know that ca, alkalinity and ph are all effected by each other. I would guess the reason your ph dropped was because your calcium was soo high. Using buffers helps prevent any drastic ph drops like you had.

 

[psumba]

You know thats what I was figuring.
I am so stupid for trying to raise my Ca more. I know better than that.
The voice in the back of my head was saying just wait till tommorrow and add the next dose.
I was guessing that the above normal dose of Ca somehow shocked it - didnt know if the pH drop was it melting or what.
I thought Ca should hold up your pH (Calcium Carbonate is a buffer isnt it?). I guess not eh.
I dont know if it will make it. It looks pretty bad right now.
Everything else in the tank is going awesome.

 

[blondenaso1]

Corbonate ions (CO3) are a beuffer. When you add buffers like seachem reefbuilder if raises alk by adding to carbonate hardness (increasing CO3 ions). When you add Ca it percipitates into Calcium Carbonate (CaCO3), reducing the buffering capacity of your tank. This dropped your alk. When you did the water changed you added water that was probably a little higher then nuetral (7.0) and with the drop in alk from the addition of calcium the pH dropped. Use something like seachem buffer to brink your pH back up and then use seachem reef builder to maintain you alk and lock it in at that pH.

 

[psumba]

Let me make sure my chemistry is working out...
Ca (+2)
CO3 (-2)
H+
OH-
pH = relative measure of OH- / H+
Therefore when I added more than recommended dose of Ca
I caused = Ca + CO3 = CaCO3
there was still too much Ca around so the next reaction was ->
Ca + 2OH = Ca(OH)2
this changed by ratio of OH-/H+ dropping my pH from 8.2 to 7.8
You know I have been doing aquariums for 10+ years (this is my second try at salt and reefs) I never needed to remember my chemistry classes.
So many things to think about...

 

[blondenaso1]

My girlfriend is telling me that Ca(OH)2 also known a slaked lime is not soluble in water. I am pretty sure that it is (kalwasser). I say that calcium hydroxide is basic and would raise you pH not lower it. What I think is that the addition of Ca lowered the alk of the water to the point where it could not sustain the pH after the water change. Anyone else?