Crustaceans dieing - HELP!

[pulik]

My crustaceans - 1 cleaner shrimp, 1 peppermint shrimp, 4-5 hermit crabs, and as of today, 2 hitch hiker crabs in my live rock are methodically kicking the bucket. Any ideas of what might be amiss?

Tank specs are: 20 gallon long (30"x12"x14"), new set-up (~3.5 weeks old), approx. 30 lbs of live rock.

Equipment: AC 70, Rio Nano skimmer, Seio 620 powerhead, 30" 36 watt coralife double linear T5 (10,000k & actinic), and 24" 48 watt Nova Extreme T5 high output (10,000k & actinic) lights.

Fish: 2 percula clowns, 1 purple firefish, 1 royal gramma, 1 catalina goby & 1 mandarin dragonet (eats frozen).

Other: 6 snails, 1 torch coral, 1 waving hand xenia, 1 fox coral, chunk of star polyp, medium sized rock covered with green hairy mushrooms, other mushrooms, 1 AWOL (though alive) anemone & 2 feather duster worms.

Chemistry: NH3/NH4 - 0, NO2 - 0, NO3 - 15-20, pH - 8.4/8.5, PO4 - 0, temp - 77.2 F.

Have been doing 10% water changes about twice a week, trying to bring down the nitrates. Also, adding ~15 drops of Aragamilk (calcium & buffer) on a daily basis, along with 2 ml. Reef Solution (minerals, trace elements & vitamins).

Everything is thriving - except the crustaceans; mushrooms are growing and spreading, xenia has grown considerably, torch coral & fox coral look great, star polyps are spreading, fish are active, eating well and have excellent colour.

Sorry about the long post, but hopefully everything necessary is listed.
...Any ideas???

[Aquattro]

Copper get in there somehow? Any brass fittings?

[pulik]

nope, and nope... thanks for the suggestions...

[dsaundry]

High Phosphates???
your water can test ok, but your rock can store high phosphate counts

[christyf5]

Hows your salinity?

[pulik]

salinity - 1.022 ...knew I'd forget something....

your water can test ok, but your rock can store high phosphate counts

How could I test to get an acurate reading if such is the case?

[Aquattro]

I know PO4 will give you a great algae garden, not sure it's ever been reported to kill inverts.

[sharuq1]

~3.5 weeks old

hmmm......did this tank come this way and was setup somewhere else and ran for xx months and you have only had it at your house 3.5 weeks? or was it just setup that fast?

Have you checked the expiry on your test kits?

Are you running any kind of chemical or mechanical media? (like carbon, filter floss, etc.)

I keep my salinity at 1.025---->I agree with Michika (missed that!)

Maybe you could get some kind of nirate sponge to soak it up (nitrate) until you find the source of what is causing it. It is possible it could be overfeeding, could be nitrate/phos stuck in the LR itself, could be in the sandbed.

On the other hand it could be you have an invert predator you don't know about? Perhaps a trapdoor snail (found one of those in my tank last night trying to eat my snail! > or a hidden crab could be the culprit....

[michika]

SG of 1.022 is probably what is doing it. Inverts need a SG of 1.024-1.026.

[pulik]

or was it just setup that fast?

Was set up that fast; used live sand from established coral tanks from the LFS, and dumped tons of "Special Blend" to cycle the tank.

Have you checked the expiry on your test kits?

Have used a couple of test kits; I'm getting the same readings from them all.

Nitrates were low to start with, therefore I suspect I'm responsible for the rise by trying to make sure the mandarine dragonet is getting his fair share.

Trapdoor snail and/or crab... Hmmm.... Would they leave the bodies lying around?

SG of 1.022.

I started with 1.017 since an LFS "calibrated" my hydrometer after having told me it was out to lunch. I have since figured out it was actually bang on, so I've been increasing the salinity over the past week and a half. Would the lower salinity have had a cumulative effect, since it's only the last 3-4 days that I've been having these issues, and the stow-aways have lived through everything (tank cycle 'n all) 'til now?

...Not trying to be difficult, just trying to figure this out. Thanks for all the input! Any other thoughts?