What happend to my live rock?

[Gary C]

My tank has been running for at least a few years. The rocks and glass sides have a coat of algae...purple and green. All kinds of worms and assorted stuff.

Today I got home one of the rocks had big white patches all over it. At first I thought it was some kind of white coating on about 1/3 of the rock. But the closer I look it looks like the algae had been scraped off or died....the rock is the size of a small child's football and the white area is facing up towards the light.

Its a 90 gal tank with a yellow tang, two damsels, and a hawkfish. Assorted crabs and snails. There was a hermit crab sitting on the rock...could he have eaten this much algae? Why would he do it now?

What else could have caused this? I added a fire shrimp and a small colt coral a couple weeks ago.....

[ckusnierek]

have you checked your CA, Alk and Mag?

[Gary C]

Honestly, I've never checked any of those...

[ckusnierek]

That would be a good place to start

Did this happen in a day or over a period of time?

[Gary C]

Happened in one day...didn't look like that yesterday. And this is the only spot....this is probably 1/20 of the total surface area of rocks in the tank....weird.

[ckusnierek]

I wonder if salt creep falling on LR could cause that?
Lets see what others have to say

[ChrisPrusha]

Do you do regular water changes?

You may want to check your pH, too.

[jenajet]

Has anything happened in the last 24 hours? For coraline to go white that fast sounds like a big change in temp or chemistry. How do the fish seem? Any coral?

[Gary C]

Originally Posted by ChrisPrusha

Do you do regular water changes?

You may want to check your pH, too.

I do about 15% change every other week...I'm due for one...but not overdue.

ph is 7.8

[ChrisPrusha]

pH is a little low, but not crazy low, esp at this time of day.

What kind of salt do you use?

You don't have a hitchiker urchin hiding somewhere, do you?

[Gary C]

for the past six months or so I've been buying pre-mixed water from the LFS. Instant Ocean mix for 18 months before that.

[ChrisPrusha]

It might be worth taking a sample of water to the LFS and asking them to test Ca and Alk.

It's weird that it happened so suddenly.

[Gary C]

Its not the water quality...it was done by a critter. The hermit crab. Caught him in the act this morning.

He was on a different rock...a small one with a colony of yellow polyps. Even without the light I could see that the rock under his feet looked the same as the other rock. And about 1/3 of the polyps were chewed down to a nub.

Is it common for a hermit crab to eat polyps?

I also had an episode about six weeks ago where a whole rock full of mushrooms was eaten. I thought it was a puffer...maybe it was this crab.

The poylps rock was only in there about two weeks. I noticed one day when the polyps were retracted there was one spot of buble algae in the middle of the colony. It came from the store that way...you couldn't see it when the polyps were extended.

The good news is the bubble algae is now gone....

[Gary C]

Anybody want a hermit crab?

[ckusnierek]

I have about 50 hermits, I have never seen them mis-behaving! weird!