Help, very confused.

[KirbyBTF]

http://img.tapatalk.com/d/13/09/04/eqededa3.jpgSo my tank has been up and running for about 6 months, it's a 12g long Mr aqua. I have zoas, xenia, Kenya trees, green star polyps, a chocolate chip star, large reef hermit, small hermits, multiple snail's, a pom pom crab, green serpent star, a condy anemone, and a feather duster. Everything in the tank is happy as can be. The large reef hermit even molted yesterday. My problem is I can't keep fish alive. This past week a clownfish died after being in the tank for only three days. A month before that a clown goby died for no reason. I don't understand how I can keep such fragile inverts but not the most hardy fish in the game. Both fish were purchased from petco...soooo that may be my problem right there. I do weekly water changes, and daily top offs. I never test my water anymore, as the bio load in my tank is almost non existent. I keep an eye out for my anemone or xenia to start wilting, luckily neither have ever had a problem. Anyone have any insight on why I can't keep fish?

Edit: Picture.

[RJT]

You really should test and post the results. The people here need that info before they can be sure how to help you.

[DopeCantWin]

Do you ever hear a loud snap coming from the tank?

[KirbyBTF]

If you're referring to a sneaky mantis shrimp, that's not the case (I wish it was!) never heard a snap in the tank.

[cakemanPA]

only guesses that I could make would be ammonia or low oxygen. Are other fish surviving?

[KirbyBTF]

I think it's low oxygen! Now that I think of it, there's very little surface agitation. Thank you so much!

[DopeCantWin]

Check the pH of the water. If it has low oxygen, it will be well under 8 at the end of your light cycle.

[KirbyBTF]

I'll check that tonight, thank you!

[young_reefer]

Good luck ... I'd love to hear back once you test and figure out if it's low oxygen.

[evolved]

There's a host of parasites which would only attack fish, yet cause no harm to other inhabitants. And they can live a couple months without a host.

[KirbyBTF]

Late reply, oops. Tested my water and was at 0 nitrites, 30ish nitrates, 180 GH. No ammonia test kit but I don't think that's a problem anyways since there's no fish in the tank. Ph was about 7.5. I don't know much about water hardness, some enlightenment would be great, 180 is a big number. If it is indeed a parasite, how do I treat for it without decimating my invert population?

[evolved]

If it is indeed a parasite, how do I treat for it without decimating my invert population?
By simply leaving it fish-less for 90 days (no "treatment" necessary).

[KirbyBTF]

And parasites can come in on any coral, rock, invert, or sand right?

[Rea17]

Yes, technically anything wet has the potential to introduce parasites, pathogens, or pests to the system and should be quarantined.

[Deinonych]

Yes, technically anything wet has the potential to introduce parasites, pathogens, or pests to the system and should be quarantined.

This.

My fish contracted crypt from a piece of coral, so I will be quarantining everything from here on out -- corals, inverts etc. Previously, I had only quarantined my fish and dipped coral before adding it to my display thinking that was enough. It wasn't.