Some Unfortunate Losses and a FULL Substrate Change - Hoping for Input from Advanced Crabbers

[jclee]

I've been keeping a colony of hermit crabs for about 15 years. When I moved across the country, they came with me, thanks to a very generous crab-sitter who was able to care for them until I was set up, and then follow directions for safely overnight shipping them to me.

As of 2017, I've had them in a 120 gallon tank. All was well, and I even adopted a couple more, since I had upgraded and had more space. They'd all be called "jumbos" at this point. Like... softball sized. Substrate is about 60/40 sand and EE. I keep humidity and temps hovering at 80 & 80%. I have a CHE that's on in, but only really in winter. (I'm in SoCal, so my apartment's often warm enough during other seasons, and the LED lights kick just a skosh of heat, so that a 78 degree apartment leads to an 81 degree enclosure.) The lid is glass, and there are bubblers in both fresh and saltwater pools. I have isopods that clean up leftover food. (Powder blues, Porcellio pruinosus.) Unfortunately, I also have house spiders that have taken up residence to eat the booming isopod colony. Most of the spiders hide behind my 3D background, but I also find them in the shell shops when I rotate out shells.

I started noticing a lot of crabs molting at once (I thought) about a year ago. I'd gone too long without rehydrating the substrate. (Yes, I know that overhead heating is known to dry substrate; with the glass lid, that really hadn't been a problem. It was my inattentiveness to blame.) It wasn't bone dry, but it certainly wasn't sand castle consistency, either. I assumed that, as usual, some were below ground molting, and I tried not to worry about it too much. At that time, I did a light turn of the top substrate, rehydrating as I went (trying not to disturb molters). More crabs came up... but not all of them. I kept meaning to do a full substrate change. I wanted to get a head count (and, frankly, to clean out the spiders. Ick.) It was so daunting, and I was worried about disturbing molters, so I did not swap out substrate or dig down to the bottom.

That brings us to today, when, sick of spiders and only having seen 2 hermit crabs above ground for a while, I tore the whole tank apart. In addition to those two visible crabs, I found 3 more molting. They are now partially re-buried in a tub w/ a bottle sunk around them each to keep them safe while they molt. I also found 4 long-deceased crabs. There were absolutely no smells. Not dead crab smell. Not anaerobic bacteria odor. My guess is that these crabs died when the sub dried, quite a while ago, and I just assumed that anyone below ground was safely molting.

I suppose I'm writing this post for two reasons.

1. For those of you with large, long-standing colonies: How often do you do a full/partial substrate change? What pros/cons do you see to this? (Obviously, I will set a much more regular schedule for rewetting the substrate, from now on.)

2. To document that this happened to me, in case others can learn from it. There are a lot of posts with the good, impressive stuff, and there are a lot of posts with the simple, beginner stuff. I don't often see much in-between. I hope this can help someone, some day.

[curlysister]

Wow! It's awesome you have had your crabs for that long - I am at almost 13 years now. I love hearing from long term crabbers!
Both of mine are underground molting right now - this is only the second time they have both been down at the same time. I can't give you any advice about having larger numbers of crabs, since I just have the two. But I dread the day they run out of energy and simply don't return to the surface. Honestly, it could happen any time. Yeah, Jonathan lived to be like 40 years old, but realistically, the dry sub may not have anything to do with it - they may have passed from old age/ running out of energy for another molt. I have never changed out all my sub, I've only added to it as I have upgraded tanks and the crabs have grown. I do know that if sub is dry, you can add a little (like half a cup at a time) poured around the edges of the tank, and it will seep into the rest of the sub.

[jclee]

Thank you for the kind words. It really does make me feel better about the whole situation. <3

I think that this is the also longest they'd gone without any real substrate change, because, having finally gotten then a very large "mansion," I haven't needed to upgrade. Every few years (until this tank), I would upgrade to a larger enclosure and redo everything. Now I'm wondering whether its like isopods, where you can (eventually) have a colony crash from built up ammonia and waste if you don't do a percentage substrate change every so often. If anyone knows anything about that, I would LOVE to learn about it.

Yes, I added water at the time, just as you describe, and the substrate I'm removing is still moist. I'm realizing it's also pretty compacted at the bottom, too. I'd turn the top 3-4" of substrate every couple of years, but I couldn't really get to the bottom 3-4" (and I didn't want to uproot molters), so it was pretty dense down there. Now I have to decide whether I'm reassembling everything with the old substrate (and maybe adding some new for a top up), or whether I am ditching some/all of the old substrate and using mostly/only fresh substrate.

[KyMart]

Thank you for the kind words. It really does make me feel better about the whole situation. <3

I think that this is the also longest they'd gone without any real substrate change, because, having finally gotten then a very large "mansion," I haven't needed to upgrade. Every few years (until this tank), I would upgrade to a larger enclosure and redo everything. Now I'm wondering whether its like isopods, where you can (eventually) have a colony crash from built up ammonia and waste if you don't do a percentage substrate change every so often. If anyone knows anything about that, I would LOVE to learn about it.

Yes, I added water at the time, just as you describe, and the substrate I'm removing is still moist. I'm realizing it's also pretty compacted at the bottom, too. I'd turn the top 3-4" of substrate every couple of years, but I couldn't really get to the bottom 3-4" (and I didn't want to uproot molters), so it was pretty dense down there. Now I have to decide whether I'm reassembling everything with the old substrate (and maybe adding some new for a top up), or whether I am ditching some/all of the old substrate and using mostly/only fresh substrate.

I am so sorry for your loss! I hope the rest remain strong and live many happy years!

[jclee]

Thank you very much. While not ideal, at least this has given me an opportunity to redo and redecorate the enclosure, which is always exciting.

[curlysister]

I wonder if some of the other long term crabbers on the Mod team might have more info about something like ammonia build up. I'm hoping they chime in here! I do know that most do change some of the sub out from time to time, or do a deep clean. I never have, I only add new sub as my crabs have grown and/or I have upgraded tanks.

[jclee]

Yes, I definitely am eager to learn anything that others know about waste buildup and/or the need for substrate changes (and frequency). The isopods are helping to tidy... but they're making waste, too, so...

*I am now rethinking my planned substrate changing % and wondering whether I should aim to swap more of it out, now.