Backyard Aquaponics
A place to discuss aquaponics

I understand that mineralization of fish poop and food is where other nutrients come from. I was thinking that if Im providing all my bio filtration via a bead filter then perhaps I could drop the gravel grow beds and do rafts in a deep water culture type thing and nft, but perhaps I need to return a portion of the solids waste to the system. So the question is how much Perhaps I could provide say 100'th or 1/10'th of the normal gravel grow bed for the purpose of mineralization and worms as a place to dump some of the solids. Do we really need so much waste mineralized? Seems we must add potassium, iron, ect anyway..

Perhaps, The solids could be drained and fed to worms and then the worm compost could be used to make compost tea which would be added back to the system for the sake of minerals and trace elements..

Any thoughts or observations on the effect of growing without using all the fish waste?

Have all the water go through a gravel filled, worm stocked barrel first - filtered, wormed, mineralised

Interesting question here, how much gravel volume does it take to mineralize 1 kg of fish feed a day? Or rather, is a gravel filter more efficient at mineralization than a gravel growbed?

I would think that low-O2 would be slower than flood/drain would be slower than having worms to eat the stuff (as far as mineralizing the "solid organic waste". That said, one could probably check on the effectiveness of worms (kg/day of waste typically consumed) and come up with some rough guidelines.

Some folks here have worms: if they have a single outfall point (where sludge would build up) and the worms take care of it, one could probably check the volume of the GB that is heavily populated and use that as a starting point...

Warning: I've never raised worms intentionally, so it's all theoretical!

Your right H - my more mature growbeds do not get ANY solids build up at the single entry point. They are very heavily stocked with large worms. The newer beds regularly need the outlet point stirred up to clear muck away, and have only a very small amount of tiny worms present.

1 lb. Worms can eat 3.5 lbs. Food waste per week, or .5 lb. per day.
453 grams of worms can eat 1587 grams of food per week or 226 grams per day.

Now I feed 1.5 pounds of feed per day, but very little makes it out the drain. So I would guess that there would be about 1.5 pounds of fish waste per day.. So if I had a grow bed with 3 pounds of worm in the gravel then all the waste would be eaten. Im not sure how much grow bed would be needed to hold 3 pounds of worm, but I suspect that a 50 gallon drum might hold that many. I know that Jaymie has sand grow beds, can't help but think worms would do better in sand or coco peat than gravel.

A sand + gravel bed with a centre standpipe + air stone would probably be a pretty good environment for worms.

I would think that the biggest problem might be water logging, so if your system only dumped solids (and water) into the worm bed every two to ten hours it might work better than twice an hour.

I know someone here had worms living in their sump so sand may not be worth the risk. I think gravel will do fine. Perhaps I will start with a 100 gallon container of gravel and return a portion of the solids to it and see how it goes..

I do know worms do just fine in gravel beds. Of course digging in the gravel beds can injure some worms but so does digging in anything containing worms.

In traditional worm bins, 2# of worms can be quite happy in 2 cubic foot of space provided the environment, food and bedding are to their liking. So a half barrel bed with 3# of composting worms would probably work just fine.

As to how much gravel bed is needed and do we need the solids in the bed for the plants. Well that discussion I know has gone round and round. Older turnkey Aquaponics systems often meant to grow only greens and other non fruiting crops, generally removed solids. Many people used to insist that aquaponics would only work for greens and couldn't grow fruiting crops. We know that is not necessarily the case now days. I think there may be something to the plants having access to the solids in a media filled flood and drain grow bed. Then again, fast vegetative crops like lettuce may not need the solids or the extra support supplied by gravel while something like tomatoes or peppers might do better in the gravel.

As to the percentage of solids returned to the system, why not dump most, if not all? You're using a bead filter, just throw the solids into the worm barrel, and have the run off go back to the fish tank. It's simple and keeps the system more closed. You could use coco for the media, (it would hold moisture, yet still drain, and would provide some level of filtration, leaving the tea [that's what it would look like] with little or no solids).

It would probably take several months for the minerals to build up in the system, but once done, there should be very little else needed. Possibly some rock dust or green sand and chelated iron.

Three questions:

I have a fairly new growbed going (about three months old) and am emptying a small outdoor fish pond. I was going to give the two inches of fish solids at the bottom of the outdoor tank to my worms but wondered if I would do better to put them directly into the growbed. Would that waste provide the minerals that have not yet had time to build up in the system or just add sludge and anaerobic spots in the gravel?

Are the minerals, etc. in worm tea accessible to the plants in an aquaponics system and if so, are they any better/worse than fish waste? I remember discussions on the hydroponics forums in which the consensus seemed to be that compost tea nutrients were not able to be taken up by the plants in those systems. Is worm tea different than compost tea in this way? Worm tea does wonders with our potted plants, should I expect the same in an aquaponics system?

Does worm tea change the balance of the water in any way? Does it have any impact on the fish?

Thanks.

Good info TCL. Greenedo I may try something like this or put coco peat on top of gravel. I am going to have a gravel growbed anyway, but I may make it much more shallow than I have now (24 inches). Perhaps just 6 (15.24 cm )inches deep. As my bio filteration will be provided apart from the gravel I should not require a deep grow bed; just enough to hold the plants up. Perhaps a 55 gallon drum with the ends cut off and filled with gravel in the end of the grow bed to provide mineralization. Then after the grow beds I will place the deep water flow area.

You may have better luck than I did, but I found that either I had water level too high and the plants rotted or that the fluctuation in water level in a 6" bed is only about 4"* and didn't work well for me. I used an autosiphon: perhaps with flood/drain (so the GB really drains fully) it might work fine. Good luck!

*(leaving at least 1" dry on top and 1" never really draining at bottom)

Just looking through this tread again. Something to keep in mind about the feeding rate of worms.
Perhaps under optimal conditions the worms could eat half their weight in feed per day but that is about the upper limit in a mature very happy worm bin. As with an aquaponic system, it takes some time for things to mature and even a mature system will slow down when conditions are not optimal (like temp etc.)

That said, the cook has been mixing up some very special stuff for our worm bin when ever we clean the "swirl" filter. We empty the solids into a large bin and wash the filters into the bin and then he collects other garden waste and stuff to soak in that ucky water and then add the shredded cardboard worm bedding to soak up the excess moisture. This mix usually makes the bins a bit too wet though for normal worm bins but the worms seem to be doing ok anyway.