Is this a good cray tank?

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knifegill

knifegill

Peacock Bass
MFK Member
Sep 19, 2005
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Oscar Tummy
Got a solid lid and gentle mechanical filtration going with a powerhead/sponge combo wrapped in mesh. They can't escape. I'm expecting to shake the babies off into another tank, so this is just for three small female crayfish. 30 gallons, 72ºF and a good mat of algae. Water is relatively hard from the gravel, but I also added some crushed coral. I think I'll use eggshells too. How hard is too hard? Any ideas? Probably another cave or two needed. They'll eat the snails, right?
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Thanks for looking!
 
For hardness, I've read that you want to aim for around 200-250 ppm KH for crays. Relatively hard, but not as hard as for corals and stuff. Keep an eye on it, I've heard adding crushed coral can spike it pretty fast. The crays will probably be fine up to around 350 ppm, but they might have some problems higher than that.
 
Hmm. My hardness test kit is really old. Do you think I can still trust it? I know it's hard because the pH is buffered really well and stays around 7.6. Does that hint at a reasonable hardness? I know, I know. Have to test it...
 
Even an old test kit should at least get you in the ball park. If you have some Distilled or RO/DI water, test that, it should read at or near 0. Then test your tap water, in most places in the U.S. it's probably over 100 ppm. Should give ya a baseline on whether the test kit is still somewhat accurate.

Edit: Tank looks good btw. Keep an eye on the acrylic lid with that light sitting on it. I've had heat from lights warp acrylic before. If there is a way out a cray will find it. ;)

If the powerhead intake is covered with a sponge, you probably don't need the mesh net. The crays will probably spend some time on the sponge foraging. A couple of mine hang out on their sponge filter for hours each day.
 
But does a sponge alone filter particulates out as well?

I'll watch for warping and escaping for sure. Thanks for the tip.

My tap water has 10 to 13 total hardness. They artificially gas it up to 7.3 and it drops into the 6.0 to 6.6 range within a day if I don't buffer it. So I know that all the hardness in there comes from the gravel and now from the calcium carbonate material I'm adding. Either way, I'll see if I can dig up the test. I don't use it because most of my tanks just have crushed coral so the pH tells my what's going on with little margin for misunderstanding. But with who-knows-what leaching out of that pea gravel, I'd better find out how ridiculously hard that water really is.
 
knifegill;4527560; said:
But does a sponge alone filter particulates out as well?
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Sponges filters alone (air powered) are fairly poor at mech filtration, except for small particles free floating in the water column. They polish the water pretty well, but larger particles settle on the substrate. Hooked up to a powerhead they might be better at mech, I haven't done that before. Guess it would depend on how porous the sponge is and how much water flow you get through it. The sponge itself would keep the crays from getting sucked into the powerhead though. Not sure what purpose the mesh net is serving? The sponge itself should keep out any particles large enough to hurt the powerhead.

If reading degrees of hardness, you probably want to aim for 12-16 DH. That would be around 200-260 mg/L CaCO3. Something in the 'moderately hard' range on most test kits.

To answer a couple other of your original questions: Yeah, you probably will want a couple more caves if you are planning 3 crays. Most crays will also eat snails. My marble crays just finished off a couple ramshorn and pond snails over the last couple days, but not before the pond snails hatched some eggs. :) Got a bunch of baby snails hanging out near the top of my tank atm. Future food I guess. :ROFL:

What kind of crays are you getting?
 
Just that certain kind of cray that everybody wants these days. I've got an Oscar to feed, after all.

The mesh is for mechanical filtration/mild polishing. The sponge on the powerhead will handle mostly biological filtration. I try to keep my water column as free of particulates as I can in all my ghetto glory. Notice the K'nex inside the bag keeping it open? Yeah. That's right. I use my old toys in my filtration. Booyah.

As for hardness, I seem to have done enough water changes to demineralize the gravel to an extent. The pH was only 7.2 today and I've been changing it regularly so it's not organic decomposition causing it to drop. I confess that I've dug through lots of boxes and can't find my hardness kit yet. Well, when the crays do arrive I'll provide them with a good acclimatization anyway. A drop or two of Prime and maybe some light aeration and then a drip line to slowly bring them into the new tank's parameters.

Glad to hear they will eat snails. Maybe I'll employ them in more of my tanks. Didn't used to be a problem but lately I'm getting tired of the bladder snails. I want the ramshorns and the other kind I have to prosper. I might pull a Noah's Ark and save the snails I want in a tank or bucket while the bladders are eradicated.
 
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