HCA: Hermit Crab Association

I am excited to be upgrading my crabitat from the 40 gallon to a 70! I picked it up for free from a customer when I worked at a Petstore.
Since I have more space now, I would really like to make their freshwater "bath" area more of a paludarium-type.((Also, despite losing several tropical and aquatic plants to these guys I am still determined to finding a good living plant that can withstand the damage of climbing... anyone have any luck?))

TLDR

Anyone have a suggestion of what type of filter to use? I would put in a bubble stone in the past, but I assume the crabs are sensitive to vibrations and didnt like how loud the pump was. I still may do a sponge-filter type or one of those whisper internal filters. Any opinions on if anyone thinks the vibrations will bother the crabs too much?

Also, I have a crawfish I occassionally give live minnows (I'm usually very anti feeder btw). Have hermit crabs ever been known to go after live fish? I understand why it would generally be a bad idea, just looking for opinions.

Thanks!

My crabs were a little freaked out by the bubblers at first but quickly got over it.

The vibrations from the pump will not bother the crabs as they will quickly get use to it.

I will mention that an decrease in total area will ultimately decrease the amount of substrate you have, increasing the chance of attacks on moulters. So id stock wisely.

As for including plants id go with pothos. They seem impossible to kill and recommended by many on here.

Live fish should not be included as often the area is too small. A min of 10g would be advised, which further takes up more swimming space.

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If you wanted to add a small filter just to keep the water fresher longer, there are very small, low flow betta filters that maaaay do the job. But I really don't advise fish.