pH spike - unknown cause - any help?

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J

Jabba954

Feeder Fish
MFK Member
Jun 4, 2009
617
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Bay Area
Hey all, today I had a big pH spike (from 8.2-8.4 on thursday to 8.8 today). The only change is that I added some more live rock (100#) yesterday after soaking it in quarantine for 4-5 days. What could cause such a big jump? I'm prepping 250 gallons for a water change tmrw right now. I did find a pretty huge shark poop in one of her caves, which I removed, but don't think that would cause a pH spike.

In the tank are still only the horn shark, grouper, and some urchins/stars. Horn shark looks healthy, and is fairly active. I added some pH buffer in the immediate.

Any help/advice?
 
Oh, other water parameters:

Salinity: 1.022 sg
Nitrates: ~5 ppm
Nitrites: 0-0.25 ppm
Ammonia: 0-0.25 ppm
Temp: 74.6 F
 
Added some generic buffer, and changed about 100 gallons, pH down to ~8.6 - still not sure what caused the jump.
 
What was the rock composed of? Some kinds of rock will leach calcium and lime into the water, creating the spike you saw. A big poop will drop the pH.
 
It was "pre-cured" Fiji live rock from the LFS - no idea of it's composition. Lots of life on it. It'd been curing in their curing vat for a few weeks, and then stayed in my QT tank for a few days. Learned my lesson.

Any thoughts on adding citrus or vinegar to the system if it doesn't drop naturally in the next day or two?
 
What was that rock that was already In the tank?
 
The previous rock was some Hawaii base rock, looked volvanic - I did the same thing to clean it up. No problem. I'll add some vinegar tonight if it's not lower.
 
BTW, just a quick update - vinegar worked very well. Note for anyone reading this for advice, a little bit of vinegar goes a LONG way. I added a single quart bottle to this tank (1720 gallons), and it lowered the pH to 8.2.
 
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