37 days - 170 gal - Snails and hermit crab slowed down suddenly, hazy water

[devitche]

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Fellow reefers, I need your advice. My Hanna checker parameters are all normal, lower side of the range. I change 20% of the water weekly; run the skimmer effectively (lots of brown gunk in the cup).

My cleanup crew was just fine until 3-4 days ago when the Halloween Hermit Crab and Mexican turbo snails just stopped being active. They move around and such, but there're no longer lively at all; rather very sedentary. They aren't starving since there's plenty of algae on the glass and rock.

Additionally, the water became a bit hazy (see pictures attached). I thought it's copepods (I can see tons of them in the glass surface), but it's probably something else. Water smells "fishy". I am at my wits end.

 

[ISpeakForTheSeas]

My first thoughts with cloudy water and low activity would be a bacterial bloom and low oxygen, so an airstone or other increased oxygenation may help.

That said, a few questions to hopefully get the ball rolling for you here to get your problem solved:

What are your tank dimensions (length, width, height)?

What equipment (pumps, powerheads, filters, etc.) do you use?

Do you have any fish and corals in the tank, or just CUC?

Can you list your specific parameters? I know you said they're fine, but what specifically are they?

Do you use RODI water?

Have you dosed anything?

Have you changed anything recently?

Is it possible that your water is contaminated by something (like copper, for example)?

Have you been feeding the hermit any meaty foods? (They're omnivores, so they need meat too).