HCA: Hermit Crab Association

My sole female crab went down to molt a few weeks ago and last year she dumped a spawn of larvae in the tiny tupperware pool I had at the time which I was totally unprepared for. I upgraded their digs last fall and I'm hoping she'll give me another this year.

I've been going back and forth on whether I wanted to try and build a filtered kreisel with their old 20 gallon similar to what the CrabCentralStation folks built for myself this year or just use the bubblers and jars and hope for the best. If I did do the filtered kreisel I was hoping to kinda make it as an insert that would fit into the 20 gallon so that it would be easy to repurpose the 20 gallon for growing out various aquatic plants over the fall/winter/spring to be placed in their freshwater pool and destroyed for their amusement.

This past week I finally figured out my issues with my 3d printer and started firing off all sorts of terrain for the DnD game I run for some of my extended family. When I was fiddling with it this morning and getting the next print run started it occurred to me that it would probably be pretty easy to design a printable cylinder with the cutouts needed for a meshed overflow and getting in for doing water changes, etc.

After my coffee I realized I should search and see if someone else had already done the design work for me and found this.

https://www.thingiverse.com/thing:4783222

If you click on the button that looks like a cube inside another cube next to the fullscreen button it will let you manipulate the model so that you can get a feel for it in 3d. Here's a video of the guy testing it in action.

https://youtu.be/jeh-cvJT_tY

I've used 3D printed stuff in my old crabitat before without issue and this seems pretty perfect outside of needing to maybe scale it up in size a bit and replace the 3d printed mesh with a purchased mesh that is finer than what is designed in or what my printer would be capable of. Is there any reason that the larvae would have issues with 3d printed stuff where the adults don't? Like plastics leaching into the water maybe? Or something else I'm overlooking?

I'm very tempted to give this a shot, especially since I'm already looking at any potential spawn as more of a learning experience for the larval stage this year. I can't see myself sourcing the tiny shells I would need for them to get to land in time and my best potential for building a transition tank right now is a tiny ten gallon that came with some Craigslist rescues. Does this seem like a reasonable experiment or should I lean towards the methods that have seen success so far?

That should work. If you’re worried about leaching I would look into what aquarists use (I haven’t followed your links), such as PET, PETT, PETG, or ABS.


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Thanks! I was planning to use ABS. In the little flow test video the guy put up I think he used PLA but then sealed it in with aquarium silicone or something similar. Yesterdays print is still going and I need to order some ABS filament but hopefully I'll be getting the print started later this week.

CleverCrabCallsign wrote: ↑

Mon Jul 03, 2023 3:31 pm

Thanks! I was planning to use ABS. In the little flow test video the guy put up I think he used PLA but then sealed it in with aquarium silicone or something similar. Yesterdays print is still going and I need to order some ABS filament but hopefully I'll be getting the print started later this week.

Please posts pics when it's done so we can see the final product!!

Took a bit longer than expected for the ABS filament to arrive but we are underway. Haven't printed with ABS before and have heard it's finicky but the first layer has happily laid down smooth on the first try.

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How exciting! Good luck!!

Looks good but how big is it? The photos seem to make it look fairly small. Water will still foul quickly if it is only a small amount as the filter won't be able to cope with the load.

Renroc wrote:Looks good but how big is it? The photos seem to make it look fairly small. Water will still foul quickly if it is only a small amount as the filter won't be able to cope with the load.

It's very small. Much smaller than I expected when looking at the model. I have another print going that I started yesterday morning with it scaled up to 150% which is about as big as my build plate will permit and it will still be smaller than I would like but I think still workable. Hopefully that will be done by tomorrow night or Monday morning.

Some more pics. First is the first attempt after it failed. At about 12% completion it was lifting off the bed pretty bad. I upped the bed temp and let it go a bit longer but ran into a nozzle clog shortly after.

Second is the second attempt with upped bed temp and nozzle temp after the print completed. It turned out pretty good but there was some visible cracking on the exterior even as it was still in the process of printing. The filter plate was also predictably a mess even before removing the supports.

Third is a picture of it sitting inside the 20 gallon which really reveals how small it actually is.

Fourth is a picture of the current print in progress. Still really a test run with light infill and a different support structure (which looks unworkable, it's filling up the spray bar). But if I can dial it in I'll do one with much higher density and attempt capping the ends and testing for water tightness.

I really wish the cylinder and spray bar were longer. I'm considering the possibility of connecting two together side by side before capping off the ends as intended to double the size.

I do really like that it has the built in filtration plate but my thinking is I would use that in tandem with a filter in the 20 gallon. That way I can have them sitting in the 20 gallon for consistent temp and filtering, pulling water from the 20 gallon through the kriesel(s) and associated filtration then dumping out into the other side of the 20 gallon to go through that filtration once more.

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Quick update, still plugging away at this. My girl is still down molting as far as I'm aware. ABS is definitely finnicky and I really feel like if I want to use it on a regular basis I'll probably need to get an enclosure of some sort for the printer. I had to take a bit over a week break with a bunch of relatives from out of country staying with us. Extra hot temps without an enclosure and young kids in the house don't mix well. But I started attempt number 5 yesterday and it's looking pretty good so far.

Attempt 7 is almost finished and I think it's gonna be the one. Gonna start experimenting with acetone vapor smoothing on the rejects this weekend as well as picking up other needed supplies assuming it finishes off nicely.

Timing is perfect as my girl came up some time in the past week. She looks to be back to her habit of hogging the wheel and sleeping in it during the day so if I do get lucky it should be pretty easy to spot if she's carrying eggs. I'm thinking that if I do spot her carrying I should turn off the saltwater pool filter and let the airstone run 24/7 instead of sporadically on the timer like it is now so if she does spawn the little ones don't get sucked into the filter but I'm still getting water movement. If for some reason that's not a good idea someone please let me know.

Some progress. Got 2 chambers to print and am pretty happy with them. The weather is dropping temperatures quickly now so I'll wait until next summer to print more. At least I should be done fiddling with the slicer software settings.

Sealed them off with acrylic panels and made sure those were water tight and then got to work sealing tubing in place. The tubing took a couple passes and I'm pretty sure I've got a leak on the piece that connects both chambers together after testing.

Hooked them up to pumps today. The first chamber is working well, sprinkled in some spirulina and it's got a nice slow circular movement off the spraybar. But it's not pulling through the filter chamber and into the second spray bar like I hoped.

My girl isn't showing any signs of carrying eggs so I think I'm throwing in the towel for now and will attempt to refine it next year. If she does surprise me I'll just disconnect the second chamber and run on the solo one I know is working. Hopes are high for next year though. I'm adopting five more cabbies at the end of the month, three of which are girls so hopefully that ups my odds a bit.

Short video of the attempt with the pumps running here: https://youtu.be/RYcS0MyoNMA?si=ro-NiL3WDWflGUih


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