Tips of rock under the sand turned black

[Instigate]

I have a 10 gallon coral and invert QT that has been up for almost a year now but just added sand and more LR from the DT about 2 months ago. I added the sand and LR because I got a pistol shrimp, a bunch of snails and some emeralds and wanted them to have lots to eat and places to hide. All went fine, had a couple emeralds die on me. But when I went to remove the pistol shrimp I noticed the parts of the rock that were covered in sand turned a black/grey color. Anyone know what caused this? Any action I should take? Tank just has 4 conch and 2 emeralds now, the conchs go in on Saturday but the emeralds still have another 20 days. In the picture I have set the rock on it's side to show the bottom.

 

[OriginalUserName]

I'd say it's due to lack of oxygen and buildup of some sulfur compounds.

Edit, yeah, some guy named Randy agrees
http://reefkeeping.com/issues/2005-12/rhf/

 

[Instigate]

I'd say it's due to lack of oxygen and buildup of some sulfur compounds.

Why would that happen in this tank and not others? The tank had 10 cerith, 5 nassarius, and 4 conch for quite a while so I'm sure the sand bed was mixed up quite a bit and the sand is only 1-2" deep.

 

[Oldsalt01]

I'd agree with the sulfur compounds. Any odor to it that you notice? Like rotten eggs? That would be hydrogen sulfide, which would be typical for an anaerobic area.

 

[Instigate]

I'd agree with the sulfur compounds. Any odor to it that you notice? Like rotten eggs? That would be hydrogen sulfide, which would be typical for an anaerobic area.

The tank water does smell a little bit but I was attributing that to my not running carbon for so long, I'm treating with fluconizole to try to get rid of bryopsis. Assuming it's sulfur, what should I do? The sand doesn't have any darkness to it. Should the rock be removed and muriatic acid bath? Just leave it? And what led to this happening?

 

[OriginalUserName]

The tank water does smell a little bit but I was attributing that to my not running carbon for so long, I'm treating with fluconizole to try to get rid of bryopsis. Assuming it's sulfur, what should I do? The sand doesn't have any darkness to it. Should the rock be removed and muriatic acid bath? Just leave it? And what led to this happening?

I wouldn't mess with it that much. Disturbing dead areas can cause problems. If it were me I'd run some carbon and do a water change trying to siphon off some of those "dead" areas. I'm not confident on the risks of siphoning though and I'd like to see what others think so don't go do that quite yet.

As to why, it could have been parts of your rock that had lots of die off when moved from open areas in your DT to suddenly being buried in the sand. Could be lots of reasons I figure.

 

[cloak]

What are your parameters? If these are OK and things aren't dying left and right I wouldn't do anything drastic just yet. Being that the tank is only two months old and your going to see all kinds of different colors & changes before things start to stabilize/mature.

 

[Instigate]

@Randy Holmes-Farley Any guidance?

 

[rkpetersen]

Question - Is the rock sitting on sand, or directly on the tank bottom? It's generally better to have the rock on the bare bottom with the sand filling in around it. If the rock sits on the sand, it will compress it and increase the chance of anaerobic areas. It's also harder for animals to burrow into sand that's sitting under rocks, and even if they do manage it, say a pistol shrimp for example, the rock may then shift slightly, trapping or killing it.

 

[Instigate]

What are your parameters? If these are OK and things aren't dying left and right I wouldn't do anything drastic just yet. Being that the tank is only two months old and your going to see all kinds of different colors & changes before things start to stabilize/mature.

The tank was setup almost a year ago, it started with just sponge filter then added some LR from the DT at around 4 or 5 months. Then two months ago I added more rock and some sand. The rock added was already matured in the DT. The top of the rock is covered in coralline algae but also has plenty of bryopsis unfortunately. Parameters are in line and no deaths in the past couple weeks. Only deaths I had in the tank was two emerald crabs died about a week apart from each other about two weeks ago.

 

[Instigate]

Question - Is the rock sitting on sand, or directly on the tank bottom? It's generally better to have the rock on the bare bottom with the sand filling in around it. If the rock sits on the sand, it will compress it and increase the chance of anaerobic areas. It's also harder for animals to burrow into sand that's sitting under rocks, and even if they do manage it, say a pistol shrimp for example, the rock may then shift slightly, trapping or killing it.

Rock is sitting on the glass with sand filling in around it.

 

[cloak]

The tank was setup almost a year ago, it started with just sponge filter then added some LR from the DT at around 4 or 5 months. Then two months ago I added more rock and some sand. The rock added was already matured in the DT. The top of the rock is covered in coralline algae but also has plenty of bryopsis unfortunately. Parameters are in line and no deaths in the past couple weeks. Only deaths I had in the tank was two emerald crabs died about a week apart from each other about two weeks ago.

Woops, my bad. Got all those dates mixed up. lol

I understand how those black areas could raise a flag, but if everything else is OK then perhaps all your seeing is just a color and nothing more. If you can remove the rocks with ease put your nose up to those black spots and give it a good whiff. Hydrogen sulfide is kind of hard to miss. Hmm.

 

[rkpetersen]

Rock is sitting on the glass with sand filling in around it.

So that's not the issue. And the rock was presumably already well cured since it came from your larger DT. Was the rock positioned differently in the other tank? Was there algae or sponge previously growing on the area that's now blackened?

 

[Instigate]

Woops, my bad. Got all those dates mixed up. lol

I understand how those black rocks could raise a flag, but if everything else is OK then perhaps all your seeing is just a color and nothing more. Hmm.

No problem, I hope so.

So that's not the issue. And the rock was presumably already well cured since it came from your larger DT. Was the rock positioned differently in the other tank? Was there algae or sponge previously growing on the area that's now blackened?

There wasn't a ton of sponge on it, some algae. But in the DT it was sitting on top of another rock and now in the 10 gallon it's in the sand bed so like @OriginalUserName said, maybe it's that. And from skimming Randy's article I could run carbon and GFO to possibly remove any hydrogen sulfide in the water. But since things seem fine I suppose I'll just leave it and let it sort is self out. Probably do a reset on the tank once all the inverts are out.

 

[Instigate]

The dark areas have lightened quite a bit since I first flipped it over. Good or bad, I don't know. Considering just putting the inverts into the DT early. But I've just got 3 more days for the conchs and would hate to risk the livestock in the tank for nothing. I wish the crabs would molt..