Keeping parameters in check
 

in a 47g mantis shrimp tank - what is the primary biological filter? I ask since I only have about 3kg (Maybe 7 pounds) of LR, and a DSB made from aragonite. I have a very small Tunze 9002 skimmer which skims almost nothing.

My nitrites is 0,2mg/L, and nitrates is 20mg/L. pH is 8.2, temp 26.4 and sg is 1.0266. Alk is also low at 4dKH.

What can I do that I can stick to monthly 20% water changes, and still have my nitrites and nitrates in check? I feed the mantis shrimp a small piece of mussel/clam/scallop/fish once a day.

What are your ammonia levels like? If you have nitrites showing up, you may have an ammonia issue too, which would be indicative of overfeeding or insufficient liverock (and the bacteria that live in it). Feeding once a day might be too much... does it eat all that you give it? Make sure you remove any uneaten food and make sure the mantis isn't burying it somewhere. I would add more liverock, probably as rubble either scattered around the tank or in the sump if you have one. That should help your ammonia cycle reach the nitrate end-product. After that, try adding a variety of macro algaes to remove the nitrates. I have a fast growing variety of calerpa and prune it regularly.

I also do 10-15% water changes weekly.

Feed every other day or every 3rd day. This will make the mantis more active also.

Add more live rock (what species of mantis?)

Decrease the salinity (won't really help with nitrates or nitrites though, just alot of mantises live in lower salinity environments.)

FWIW 20 ppm of nitrates is acceptable for most mantis tanks depends on species)

Dan

Cool - I have read somewhere I need to feed them once a day, but that felt wrong since the mantis only seem to take the food once every second-third day anyway.

So I know I have overfed a bit. Is it better to add LR to my (small) sump, or a DSB in there? I assume adding the caulerpa to the main display is fine.

It is two peacock mantis shrimps.

I think live sand is a great thing, but would probably go with the live rock first. Choose low-density pieces with lots of holes and empty space inside rather than the dense type. Skeletons of coral like torch and plate coral seem to work much better than acropora. Also make sure you have plenty of liverock rubble in the tank itself for them to build their tunnels. Are they both together? Not in a divided tank?

I have an acrylic divider to separate them. Currently each one has dug a burrow beneath a big piece of LR.

Ah, ok.

It sound like changing your feeding habits may be enough to fix things. Do a water change and give it a week to see if your nitrites (and ammonia?) drop.

If not, add as much live rock to your sump and tank as is convenient, and do another water change. Maybe add some macro algae for nitrates and then see how things are in another week or two.

Hope that helps!
Greg

Thanks for your help!

Just had a thought... you may already do this, but make sure they get a live crab or snail to "smash" on occassionally to keep their rapts in shape.

I do... Sad thing is I found one crab - sliced it in two (the one mantis lost both his raptorial appendages) but that was the day before he molted - I did not realise he was about to molt. So that was one crab wasted :(

At least now he has two 50% functioning raptorial appendages. The little one caught 2 crabs and killed them thus far, and is constantly creating a hollow in the LR using his appendages.

OK, first if you have only 3 kg live rock in a 47 gal tank, this is woefully inadequate. You need lots more rock! I would think that an additional 15 kg or so is called for. Additionally I would at least double your frequency of water changes. Any measurable nitrite is toxic. The low alkalinity can be boosted through additives such as a buffer or other alkalinity supplement.