My experience with blackworms is with keeping them in a heated aquarium ~76ºF, in a deep sand bed, with fish, snails, and the occasional shrimp, so my advice may or may not be worthwhile.
One thought is: cycling a tank takes much much much longer at lower temperatures. Perhaps you could try heating it. Also, worms' metabolism is far slower at 55F than in the high 70's and low 80's, so growth and reproduction (mostly by just breaking and the pieces regrowing their lost ends- stir them briefly but vigorously once a week and their numbers will grow dramatically, quickly) will be low if left unheated.
I should perhaps emphasize cycling. If you don't want to have to perform frequent frequent water changes, you must consider cycling the tank, at a warmer temperature so it takes less than a year, and if you want to use a filter, air driven or power, you may want deeper water, especially with air driven foam filters, which depend entirely on the bubbles drawing the water up behind them as they rise in order to produce the suction which pulls the water through the sponge. Not only will you get better suction with deeper water up to a point, the water will circulate better throughout the tank rather than forming a smaller, local convection. Anyhow, yeah, don't let those worms near a filter pad or sponge - neither you nor they can extract them. However, since you are using a pile of gravel for them and not sand or muck or a layer of decaying plant material, a filter with good surface area (I think sponges are pretty good, not great, but pretty good)(sand is an order of magnitude better, even without air or a powerhead driving water through it) the only good site for masses of nitrifying bacteria to settle on would be the filter. Were I you, I'd consider removing the gravel and replacing it with good mud. If you want to try this and don't have good, wholesome mud from an unpolluted pond (and even this may contain some parasites and diseases which may hassle the worms) you can try some really rich topsoil sold without any amendments ( added sand, vermiculite, peat, peat moss, or anything else that's not soil) or possibly mushroom compost, which is super yummy rich in nutrients. OR you could try sand. Pool filter sand is my suggestion as the easiest to find, pretty cheap, not prone to compacting, easy for the worms to dig down into, and excellent as a biological filter. For worms, I'd use anything from 1.5" to 3" or 4" deep a bed of sand. To get them started, as the sand bed tank cycled, I'd toss in a few algae wafers - those wafers for suckermouth type fish like plecos and otos but which all the livebearers seem to eat before the suckermouths do. The wafers will provide a great source of ammonia as they decay, and they will disintegrate and become host to a huge amount of bacteria. Once the wafers are all totally disintegrated and the ammonia and nitrite are 0, through in the worms. Maybe stir the decayed wafer - mulm into the sand a bit first. If you'd like to keep the water shallow and not use a filter, the sand bed or mud and perhaps clay is the way to go. Try to get Anoxia to write about clay and what she thinks it might be like as a bare substrate for blackworms, she is the clay expert. Anyhow, a cycled tank with a fine grained substrate will be a good biological filter and if deep enough can start denitrifying pretty decently, keeping the nitrates down, which isn't vital but can be a good thing.
The thing about gravel is that it isn't a good biofilter because the grain size is much too large to sport the sort of surface area sand or finer grained media have. Also, it holds mulm in itself in clumpy lumps and sand and finer only allow very small particles in, where they slowly settle and feed lots of bacteria, which the worms enjoy burrowing down into the substrate to feed on, leaving their tails to wave, up beyond the surface of the water if it's shallow enough, to have access to better oxygenated water or to air. Worms mouths are very very small, too, so they don't deal well with larger chunks of decaying organic debris unless they're truly mush. The sand etc. you will see, becomes completely infiltrated with decaying stuff to the point where stirring it raises a dusty haze, quite thick. The worms love that stuff.
Eating decomposing maple leaves makes sense to me; lots of bacteria and once the decay really gets underway, soft and mushy organic material. Or, you could use some flake fish food. OR, algae wafers. When I toss one into my invert tank, the next day there is a forest of worm tails surrounding and penetrating the wafer. The worms really really really like them! I think the brand I have is Hikari. Anyhow, the wormies travel through or above the sand and come up from beneath it, it seems. Never seen 'em move 'cause I sleep while they creep. You could probably make a culture out of unbleached toilet paper or paper towels allowing them to rot in a pan of shallow water. You'd have to change water and paper quite a bit I'd guess.
Boiled carrot? That makes a lot of sense, especially if it was boiled until soft.
Oh, the think with a cycled tank and worms, you can't do it and raise vast numbers. Sure, hundreds and thousands, but they seem to produce a lot of slimy waste which they'll choke on if it can't disperse and decay into nonexistence. In super-dense numbers, the biofilter cannot keep up, as it couldn't with any critter. Dense cultures require very regular water changes. And they are kept a little warm. 55F is more like a high temperature for storing them at I believe. Keep 'em even colder and they'll hardly have metabolisms so won't foul their containers quickly.
In my invert tank, which has a 3.5 inch bed of pool sand (bottom 2.5") and this big grained sand of about 1 mm diameter grains for the top 1", I have hundreds and hundreds of blackworms. They are preyed upon by the occasional dwarf shrimp like rcs or tiger shrimp, but otherwise are unmolested until I use a turkey baster to harvest 'em. I suck up a bunch of sand and point the turkey baster down, hold the tip closed, and shake gently, but enough to cause the sand and worms to sort of mix into the water, then the sand settles down to the tip and the worms follow. I take my finger away from blocking the tip and shake gently as the sand falls out and the worms drift down after, slowly. I just remove the baster with worms and squirt 'em into the fish tank (the one with the fish, not shrimp) and watch my nanofish go nuts. Just that easy harvest method has me a permanent sand fan.
If you're not trying to feed a lot of worms to your fish frequently, you might want to try the approach with the sand. It doesn't require the addition of any other critters or plants and is pretty easy. Especially since it isn't really needing to denitrify - just nitrification and being a matrix for mulm and bacteria which the worms burrow through and eat. Don't worry if anyone tells you there will be anaerobic decay in it and that it will release hydrogen sulfide and kill everything. I've ever only read on "it happened to me" story, and it didn't involve a deeper bed, composed of larger and evener grains as is pool filter sand - sand which allows the bacterial processing of such toxins into harmlessness before trouble. I've kept them for a long time now and had no problems. Just avoid fine and unmeshed sands and you'll be fine if sand's the way you want to go.
With a 10 gallon fishtank, if you add heat, sand, the algae wafers, and remove the gravel or just bury it, you might as well add some rcs or crs or tiger shrimp, bumblebee shrimp, any kind of dwarf shrimp - they are incredibly light on the bioload, eat very few worms, not enough to impact their reproduction terribly much. Toss in a big wad of java moss and you're in shape. EXCEPT you might like to get a light for the java moss to be happy. I keep mine in a 5.5 gallon fishtank and they've been self-sustaining and providing worms for 19 fish of about .85 to 1.2 inches long, nonstop.
Most basically, I say warmer water like above 75F is good, keep the water fresh however you like, use algae waters or fish food to feed 'em. They'll be very happy eating decaying organic matter any time it's full of nutrients. If the water is too deep for them to stick their tails out into the air, make sure it circulates well throughout the whole tank - O2 levels can crash from these worms' decaying waste and their own metabolism, and CO2 levels can skyrocket if the water doesn't turn over fairly often. If you have a very dense culture of the worms rather than my more laid back dude ranch for worms in the 5.5 gallon, they'll easily suffocate in their own filth without daily water changes and circulation.
I'm now so far past my bed time that my eyes are too crossed to type any more. I hope this made some sort of sense to you, the reader. CIAO!
Hey,
It isn't even a great filter concept, just an airline shoved into the middle of a small aquaclear sponge and left to bubble. Meant solely for biological purposes.
