Help please… crustaceans have been dying

[dbr1206]

Hello everyone,

I initially started up my 15g nano reef tank in December 2022 so I could get saltwater inverts, as I was interested in them. However, I have had crustaceans dying one by one, with about 2+ weeks to one month intervals between deaths. I have tried everything to figure out what’s wrong and nothing has worked, so I’m going to try to list out the deaths chronogically as a start.

1-2: Blue leg hermit crabs disappear mysteriously (around March)

3: Black porcelain crab that had been in the tank months is found dying at the back of the tank, upside down. Perhaps during an attempt at a first molt? (Around the end of April)

4: Halloween hermit crab stops moving, a few days later I checked the shell and the rotten crab body falls out. No sign of ever leaving the shell, and there are no other cone shells in the tank. (Around early May)

5. I find my fire shrimp, my favorite invert, dead in the back of the tank. It had molted successfully many times before, but this time I found a molt with the shrimp still in it, only the tail meat remained at this point, as the rest had been consumed by hermits. (Late May)

6. A blue leg hermit molts successfully, and I see it in a new shell it had selected. A week later after a vacation, I find the shell in the same spot but completely empty, no sign of the crab anywhere. (June)

7: Blue leg hermit crab found molted successfully, but nearby is the crab, outside of a shell, still holding on to life as its soft abdomen had been ripped open, and it was missing a leg and eye. (July 1st)

What I know so far:

All deaths are probably related to molting.

My water parameters are great at all times. I test every week, change 15% of the water every week. My nitrates are never above 5-6ppm, and my phosphates are always at safe levels.

The deaths are inconsistent, if they were caused by bullying from hermits, how did the fire shrimp molt successfully so many times and how did the Halloween crab die while protected from blue legs inside its own shell?

My only fish is a healthy juvenile banggai cardinalfish which never touches anything.

I have a stable population of pods.

I keep live coral (softies and LPS) and I have never once had a problem with them ever. They have been healthy since the day I got them.

Other crustaceans in the tank have molted fine at the same time that another died trying.

The tank used seeded dry rock, no imported live rock with hitchhikers was used.

There are plenty of shells for the blue leg hermits to live in and choose between.

———————————————————
I honestly have no idea what to do now. Everything seems perfectly fine in my tank and it’s so frustrating that I don’t have an answer. I am down to 1 last blue leg hermit. I hope someone out there has an answer for what is happening and what I can do. Thank you.

 

[blaxsun]

Are you feeding your crabs?

 

[dbr1206]

Are you feeding your crabs?

All the inverts, including the crabs, were fed. The shrimp ate like a pig when it was alive. The crabs ate algae and mysis, they were part of my CUC.

 

[blaxsun]

All the inverts, including the crabs, were fed. The shrimp ate like a pig when it was alive. The crabs ate algae and mysis, they were part of my CUC.

You may want to try augmenting feeding with a small piece of seaweed rubber banded to a small rock,

 

[saltcats]

Checked calcium + alk levels? Anecdotally low iodine can be associated with molting failures but it seems inconclusive whether supplemental dosing helps.

At least one moult failure sounds like it was just attacked before it could get back in a new shell safely. The one you saw get in a new shell and then found that shell abandoned later may not have died; sometimes they do just swap shells!

 

[FishKeeper.mp3]

do you dose iodine/calcium/dKH?

 

[Stomatopods17]

I think I can answer some of these, but; is any of your equipment used bychance? Copper is a silent killer if you have anything rusty or potentially treated by a past owner leeching out.

Dinos can also be very toxic, so if you have a dino outbreak and your inverts are eating it, it can be a bad time.

1-2: Blue leg hermit crabs disappear mysteriously (around March)

Blue legs will perish if there isn't enough shells, especially speeding up the process by killing each other for them.

3: Black porcelain crab that had been in the tank months is found dying at the back of the tank, upside down. Perhaps during an attempt at a first molt? (Around the end of April)

Porcelains are deceptively tricky. They're filter feeders and need fed like filter feeders, you have to spray them with phyto, coral food, etc. they catch food in the water column with their little fans and are constantly filtering it. Your tank is still too newish for them to survive purely from that, so you'd have to supplement them better. Its actually normal sounding that you have them for months and likely starved later.

4: Halloween hermit crab stops moving, a few days later I checked the shell and the rotten crab body falls out. No sign of ever leaving the shell, and there are no other cone shells in the tank. (Around early May)

They need cone shells exclusively, kinda a pain, but personally I never had luck with halloween or blue knuckle hermits. Don't know why and I'd be willing to make a thread asking others how the story goes with them cause my experiences with them seem to repeat.

5. I find my fire shrimp, my favorite invert, dead in the back of the tank. It had molted successfully many times before, but this time I found a molt with the shrimp still in it, only the tail meat remained at this point, as the rest had been consumed by hermits. (Late May)

6. A blue leg hermit molts successfully, and I see it in a new shell it had selected. A week later after a vacation, I find the shell in the same spot but completely empty, no sign of the crab anywhere. (June)

unsure on these

7: Blue leg hermit crab found molted successfully, but nearby is the crab, outside of a shell, still holding on to life as its soft abdomen had been ripped open, and it was missing a leg and eye. (July 1st)

That sounds like the molt itself.

My water parameters are great at all times. I test every week, change 15% of the water every week. My nitrates are never above 5-6ppm, and my phosphates are always at safe levels.

The deaths are inconsistent, if they were caused by bullying from hermits, how did the fire shrimp molt successfully so many times and how did the Halloween crab die while protected from blue legs inside its own shell?

Starvation is obvious on the porcelain, hermits could be related to overstocking them and them killing each other for shells (Usually in my 125g there's die off until only 3 hermits are left then I have them a year or two, much less in a 15g.), keep an eye on temperature and Ph swings, ESPECIALLY at night, you'll see Ph do a lot of weird things when adding an air bubbler, when night time rolls around, and oxygen isn't consistent.

Fire shrimp is the only one I can't narrow down, but could be the 'it happens' case of this. Its very possible it just had an unsuccessful molt, or got really beat up by the waterflow. If you don't have the overhangs for one (which to be blunt, fire shrimp are notorious for being invisible once added to a tank so if you're seeing it a lot that might be a red shr- flag.) its possible it stressed out or flow got to it after a molt.

My only fish is a healthy juvenile banggai cardinalfish which never touches anything.

I doubt it was a culprit, but FWIW I had a banggai cardinal go rouge and eat my sexy shrimp despite living together for months, but pretty sure it was a size related thing.

Other crustaceans in the tank have molted fine at the same time that another died trying.

FWIW crustaceans all have unique molting requirements. Some are just more forgiving than others but most deaths due occur from molts going wrong or improperly planned around (mantis shrimp almost always are killed from molts with inadequate burrow setups, and there's still a good chance they fail at it with the proper setup.)