Backyard Aquaponics
A place to discuss aquaponics

The problem here seems to be mechanical filtration. Basically you should be able to vacuum your raft beds with a powerful pump, the only ? is the filter. It would be nice if we had cyclonic shit catcher like on vacuum cleaners when you do your carpet.
However, if we take a step back to the old vacuum cleaners which used disposable bags then what do we get?

MattyYoga (?) was using bark chips as a mechanical filtration media (I have been doing a bit of research on this). They are relatively cheap and when the bag gets full you actually have a salable (with a little extra work) product.

Anyway just imho.

I like this idea and hope to hear more on this Sleepe. I assume fish wouldn't want bark with a lot of sap like there is in pine bark. Nevertheless, I use pine bark to help bring the pH of our garden down by using bark as mulch I wonder if there is a small amount the fish could handle? Although it sounds like you are suggesting an off-line application here. Still it's got my curiosity up.

Actually Brian I do intend to use it as an online application (although this one was just a vacuum the DWC).

At one stage I used to grow orchids, mainly cymbidiums, and it pissed me off the amount I used to pay for potting mix so I used to get graded hardwood chips stick them in my cement mixer with water some ammonium nitrate or urea and a handful of blood and bone. Stick them in one of those large black garden garbage bags and park them in the garage for about 6 months.
Cost of graded hardwood chips has gone up a lot, about $100 cu m but there again orchid potting mix is about $30 for about 30l.
Using the chips in in a filter (1" graded) I will need about 6 cu ft but then only rotating 3 cu ft per filter change. They will already be starting to break down or at least softening when I take them out, probably still need some urea as they are high carbon .
So 1 cu m (about 35 cu ft) should last me quite a while and as an end product I can take up orchid growing again or sell it.
That was rather a long post for me.

I have a small raft system (4'x8'X 10"). I use a small pump and pump the soupy mess directly into the garden bed. The use of gravel was mentioned. Should I use a gravel bed in the raft system. All my grow beds are clay pellet type.

Thanks for all the information y'all provide.

I'm not sure I understand but if you mean using gravel in the DWC channel, it would just make it harder to clean and isn't necessary so I don't think you should do this.

On the other hand if you're talking about using a media bed (gravel or clay pellets work just as well) as a prefilter to remove solids before the DWC then yes you should or else you need some other filtration to remove solids (static upflow filter works). The suspended solids will cling to the plant roots and deprive them of oxygen if you don't.

Just thought I'd ask about the gravel, you know, anything to improve the environment in the bed. I don't have anything in the raft basin only flowing water. The build up of muck or is it algae. This is my concern. From what I've read, I should clean the bed once a year. Is this a safe idea?

If you're getting a buildup of muck and don't already filter the solids before the raft bed I'd add the filtration mentioned earlier. Cleaning is a necessity but can cause problems - You should clean the bed and I'd do this by first disconnecting it from the rest of the system since this can liberate toxic gasses as you stir the settled solids to remove them. I haven't tried this but you could probably filter the water through a Static Upflow Filter and pass it back into the trough but aerate it well to remove any toxic gasses before running it through the rest of the system. Other than that suggestion I'd look back through this thread and others to see what other people have done - but definitely clean the raft bed of settled solids if it needs it (whether you've used it or are currently just running the water through it).