I have a pond with a bio and settling filter that I clean about twice a year yeilding about 20 gallons of sludge comprised of fish detritus and other decomposed organic matter.

I usually just pour the sludge out in my grass yard or around some flowers adding much water to help it spread. It has never burned any plants, so I don't think it is like raw chicken, horse, or cow manure. It holds moisture well, but when completely dried, it turns into a fine-grained very hard brick.

I wonder if there would be any drawback to my mixing it in with the soil in a newly built raised garden bed before transplants and seeds are installed. Into my top 5" of clay, I've already thoroughly mixed in the equivalient of 2 1/2" of compost, 1 1/2" of peat, and 1/2" of sand.

The sludge would spread about 3/4" thick, but it's likely 2/3 water. So that means I'd be adding about 1/4" of solids, and I'd mix it in about 4" deep.

If direct to garden is a bad idea, should I just add it to my pile?