Emerald Crab Picking at my GSP Frag

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wwarby

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Last night I caught one of my emerald crabs picking at my GSP frag. It was all closed up and I couldn't see whether he was picking algae off the frag or if he was nipping at the polyps, but it does look slightly worse for wear on the side he was interested in this morning.

Last night:

This morning:
IMG_3079.jpeg


I've read that under-fed emerald crabs might exhibit this behaviour. I'm relatively new to the hobby - only three months in so far. This tank previously had a mantis shrimp in it which I've now moved, so I'm starting the process of turning it into a mixed reef tank. It currently has no fish (fish to go in will be clowns, currently in QT) and just three new softie frags but over the course of last week I've added quite a lot of clean-up crew:

1 boxer shrimp
2 scarlet skunk cleaner shrimp
2 blood red shrimp
2 peppermint shrimp
2 emerald crabs
2 zebra hermit crabs
1 conch
1 turbo snail
1 tuxedo urchin
3 bumblebee snails
3 nassarius snails
3 spiny astrea snails
3 money cowries
10 trochus snails

I was advised by an LFS that I trust that it would be fine to go quite heavy on the CUC stocking because they have a very low bio load, it's a decent sized tank (64 gallons) and at the time there was plenty to eat in there because the rock was covered with green algae. I was astonished by how quickly they picked the rocks clean - within 72 hours there wasn't a scrap of green anywhere on the rocks or the glass (they've even cleaned my Flipper and filter intake). The LFS said this wasn't a problem and I could supplement their diet with pellet food, so I started feeding them about this much pellet once a day (just dropping it into the tank and letting it float or land randomly, since my CUC are spread all over the tank):

IMG_3082.jpeg

The LFS said this was way too much and it should be more like 4 of 5 pellets every other day, but I wonder if they were thinking I had a different sized pellet because the amount I'm feeding seems miniscule for the number of mouths it's shared between.

All the inhabitants seem happy and healthy - water parameters are mostly good - no ammonia, 0.01ppm nitrites, 25ppm nitrates, 0.07 phosphate (down from 0.2, I'm reducing it with Rowaphos), salinity 1.025. I know my nitrates are a bit high and for that reason I'd like to limit feeding, but if my crabs are hungry enough to nip at my corals I'm wondering if I'm feeding too little?
 
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Cali Reef Life

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I think a strategy you can go is nori seaweed and lower the pellets to a few. Crabs are opportunity eaters. No alage they will eat to survive. The pellets probably get lost and that is a lot for no fish. I would place a nori sheet small bits of it and a few pellets. If crab continues to be bad place In sump but gsp grows faster then almost any coral so it should out grow his eatting. Are you planning on getting fish?
 
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wwarby

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I think a strategy you can go is nori seaweed and lower the pellets to a few. Crabs are opportunity eaters. No alage they will eat to survive. The pellets probably get lost and that is a lot for no fish. I would place a nori sheet small bits of it and a few pellets. If crab continues to be bad place In sump but gsp grows faster then almost any coral so it should out grow his eatting. Are you planning on getting fish?
Thanks - I'd heard nori might be a good shout, I'll pick some of that up tomorrow. No sump in this system unfortunately (cannister filter) but I can put the emerald crab in my QT tank if necessary, at least as a temporary measure (it's more of an observational tank - I'm not treating with copper as the fish I'm buying are all copper treated in the LFS). The QT has two lumps of live rock covered in algae so he'd be doing me a favour in there and I can always move him again if I need to copper treat that tank.

Yes, planning to stock with fish gradually. Got two small clowns in QT now going into the DT in a couple of weeks but my QT tank is small so I'll only be quarantining one or two fish at a time and it's going to take a good few months to get up to full stocking.

Not seen really any growth at all on the GSP so far, but it's only been in there for a little over a week and my lighting isn't very powerful (I'm waiting on delivery for two second hand ReefLED 90s to replace the Fluval strip light which should improve coral growth hopefully). I'm gonna be putting more corals in there though, so don't want the crab getting any ideas about eating other corals. I'll try nori and see how I get on with that and keep an eye on him.
 
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Yeh, I'm 3 for 3 with emeralds lately snipping the closed polyps off of my Zoa's at night, not even eating them, just snipping them off and letting them fall to the sand. So, no more Emerald's in that tank. I target fed them daily, so it wasn't a food issue.
 
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I’ve moved the offending crab to my QT/observation tank for now. I bought some nori yesterday to give the inverts a bit of extra food until I get some fish in there and there’s a bit more going on for the CUC - I have another emerald in the tank so I’ll watch him and see if he behaves himself.
 
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I'd watch those peppermint shrimp, too. They can sometimes behave badly.

What kind of pellets are those? I have a heavy CUC and I drop in a broken half of an alge tab every now and then, especially for the two conches. But I limit the fish pellets like TDO or NLS (drop one or two around the nassarius) because they are very concentrated and add a bunch of nutrients into the system.
 

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I had a conversation with your emerald crab... He said he was just trying to help you out, because the GSP can become a pest coral. He said he was prepared to even take the fall for your new reefer decision.... :beaming-face-with-smiling-eyes:
 
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I had a conversation with your emerald crab... He said he was just trying to help you out, because the GSP can become a pest coral. He said he was prepared to even take the fall for your new reefer decision.... :beaming-face-with-smiling-eyes:
Love it!

I’m well aware GSP is seen as a pest, but so many of the corals available to beginners are drab ugly splotches of brown and beige so it’s not hard to see why fluorescent green grass that grows like a weed appeals to newbies like me! I may live to regret it but I’m sticking with the GSP for now :D
 
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I'd watch those peppermint shrimp, too. They can sometimes behave badly.

What kind of pellets are those? I have a heavy CUC and I drop in a broken half of an alge tab every now and then, especially for the two conches. But I limit the fish pellets like TDO or NLS (drop one or two around the nassarius) because they are very concentrated and add a bunch of nutrients into the system.
Thanks for the heads up on the peppermints - I’ll keep an eye on them. Photo attached if the pellet pack. I’ve stopped using them for now as my nitrates are already about 25ppm and don’t want to make that any worse. I did half a sheet of nori the other day. What do you mean by now and then? I’m still learning about how much to feed - it’s hard to wrap my head around just how heavy those pellets are - I have like thirty five mouths to feed in there and the pellets are tiny. Nori does seem like a better food in general but maybe I’ll try to do pellets just for the conch?
 

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bnord

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Love it!

I’m well aware GSP is seen as a pest, but so many of the corals available to beginners are drab ugly splotches of brown and beige so it’s not hard to see why fluorescent green grass that grows like a weed appeals to newbies like me! I may live to regret it but I’m sticking with the GSP for now :D
Nothing fundamentally wrong with GSP. There are a variety of growth types, shades and even patterns

Whats wrong is when they are given free access to the main scape - where they can and do take over every space available

I put them on magnetically mounted floating rock islands and they great for color and flow - pic below is an example

and i for one add 1-2 female emeralds if i ever sense i have lost one.
Only place i have ever seen Valonia is the power heads or backs of trochus. Hasve watched them destroy Valonia within a minute of placing them on an infested rock. Have watched them look like they were picking on polyps, but have never seen any ill effect to the corals.Think they are still picking algal film. I know they are accused of all forms of evil, but i still consider them important CUC community members.
image.jpg
 
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