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Natural Saltwater Crab Tank

We setup a 10 gallon saltwater tank. The idea was to have an all natural setup with local creatures taken from the ocean. We also wanted to use the exact same water, stones, gravel, sand, and plants from their natural environment. We gathered all of these things from the local beach and rocky shoreline in NYC and Long Island.

Natural Saltwater Tank Setup

We used water scooped directly out of the ocean. This works short term as we can just scoop more water from the ocean any time we need to add or change the water. To be sustainable long term we would need to create our own salt water.

As a substrate we used gravel taken from the beach (large smooth stones). This works nicely but doesn’t give a huge surface area for beneficial bacteria to grow making it harder to establish an ecosystem. The other disadvantage to the gravel/stones we used is that they are so large that the hermit crabs would tend to get lost among the stones making them harder to observe. We are going to be adding sand to the tank. At least part of the bottom will be covered in sand.

We gathered various types of seaweed form the ocean and added them to the aquarium. We anchored them to the gravel substrate. Initially the plants were in relatively good shape but the crabs started picking at them and after a few days they started appear a bit damaged.

Tank and Equipment

We are using a small 10 gallon tank with no hood. The tank itself only cost $10 USD for just the tank and nothing else. We used an existing aerator I had in my closet. I basically just ran a tube into the tank and that’s it. Without aeration the aquarium inhabitants will not last long so this is absolutely essential.

Filtration System

We didn’t include a filtration system initially since we have easy access to sea water. The plan is to do frequent water changes using natural water from an already established ecosystem. We basically just use the water taken from the natural environment. We are eventually going to need to setup a proper filtration system with a protein skimmer if we want to keep this tank setup long term.

One thing that we won’t need is a heater. We are never going to need a heater for this tank since it is a temperate/cold water tank. Every inhabitant of the tank has been taken directly from the ocean in or near NYC and Long Island. Their natural habitat gets icy cold in the winter.

Aquarium Lighting

Since we didn’t include a hood we also didn’t include any lighting. This is kind of ‘suboptimal’ for several reasons. First of all, we can’t see the inside of the tank very well. This also makes taking pictures or recording video harder. We used a temporary light light to record our videos. The plants are going to need light to grow well(if the crabs don’t tear them apart). The crabs themselves don’t really need a direct light source as they tend to be nocturnal anyway. They are most active when all the lights are out. We are going to need a real lighting solution. Ideally I would like to construct a custom tank lid and build in my own lighting system.

Tank Inhabitants

We captured several different aquatic animals to live in our tank. Some would become permanent residents and some would be released back into the ocean. We have/had the following:

The Spider Crab

This was one of the largest things in our tank and it looked really, really cool. It was relatively small for a spider crab caught in this area but it looks huge in a 10 gallon tank. It was much larger than anything else we put in there.

It had seaweed growing all over it.

It turns out that the spider crab had a ton of eggs. We didn’t see any sign of this when we first captured it but after being in the tank for a few days the eggs became visible. Due to the eggs we decided that it would be best to release this crab back into the wild so that it could reproduce. I don’t know the first thing about crab eggs and reproduction and the chances of all of those eggs surviving would be pretty slim.

Hermit Crabs

We collected a bunch of small hermit crabs from the beach. We mostly found them walking around in shallow water in an open, sandy area away from the rocks. They get lost amongst the rocks in my tank so I’m not sure how many are actually in there at this point. Once I clear out part of the bottom and add sand they will be easier to observe. Currently they just wander around the tank looking for food. The are relatively active and are pretty neat to watch. They will scavenge up any small bits of food left in the tank.


The snails were just about the easiest thing to find. Some of them were collected in sandy area of the bean while most of them were picked off of the rocks. They are much easier to find at low tide. Aquatic snails don’t sound like the most interesting things to watch but they are. The are more than just ornamental. They often move around at a pretty steady pace and spread out inside the aquarium. It is pretty neat being able to watch something moving around while stuck to the side of the glass. When you look closely they have really neat looking eye stalks and appendages.

Green crab

Last but not least, we collected a single small green crab. We are 90% sure that we’ve identified this correctly as a green crab. There is probably about a 10% chance that it is an asian shore crab.

I’ve caught hundreds of crabs that look just like this in the past. They hide amongst the rocks near the edge of the water. You can find them by flipping over rocks at in tidal pools. It is easiest to find the at low tide. Sometimes almost every rock that I flip has at least one of these crabs hiding under it.

This particular one hids amongst the stones on the bottom of the tank most of the time. He crawls around a bit during the day but gets active when the lights go out. He has generally not harmed or interacted with the other inhabitants of the tank at all as far as I can tell.


Feeding the crabs has been interesting. Before we let the spider crab go we dropped a big chunk of duck meat into the tank. She grabbed it immediately and started devouring it. She held onto the meat and pulled it apart piece at a time. The hermit crabs all gathered around to pick up any of the scraps that fell off. We filmed this up close and it was one of the coolest things I’ve seen in awhile.

We captured the feeding as part of our first crab tank video but we also posted a separate video containing only the feeding. Here it is:

Smaller Snail Tank

We had also previously setup a tiny 2.5 gallon planted snail tank. The tank was small and the plants weren’t doing very well. The snails were fine so long as they had oxygen in their water. I made the decision to merge this tank with the larger (but still small) 10 gallon saltwater tank. I pulled out all of the snails and placed them in the larger tank. They picked right up where the left off and kept crawling around. I also moved the aerator from the 2.5 gallon tank over to the 10 gallon tank. They were both vaguely equivalent but one seemed to make less noise and had an air stone / air diffuser.