Raft or media

[Pete]

I am a newbie trying to learn more about aquaponic.  These are the little that I read up about media or raft:

1.  Media can also act as bio-filter so going with media eliminates the need for a seperate bio-filter. 
2. Deep-water-culture (DWC) needs bio filter.
3. Going for DWC saves buying lots of media.
4. Rule of thumb for media and fish tank volume is 1:1.  Not sure how DWC calculate that ratio?
5. I read that DWC needs highly oxygen saturated water to work, at least to thrive.  Need addition energy in addition to water pump to drive air pump?
6. In case of power outage.  Plants in media may last a bit longer as media can stay wet for awhile.
7. How about DWC?  In case of outage, do the root remain submerged in water or water actually drains from troughs or channels  when not being pumped?  
8. Do some plants grow faster and more vigorous with DWC? May one assume that plants may have preference? some do better in media or others in DWC?

OK, that's all I can think of.  I am wondering if one can have a combo system?

Thanks for helping.

 

 

[TCLynx]

1 and 2 yes basically correct (though there are some very low stocking density raft systems without extra bio-fitlers.)

 

3) You might not have to buy a truck load of gravel but Remember that DWC requires the Rafts and the net pots and media for the net pots and can require extra work in starting seeds then putting them in the rafts.

 

4) for all systems you have to balance your fish load to your filtration capacity, this can be fairly easy if you keep your fish load small then a 1:1 media system works and if you want more fish you can go twice as much gravel as fish tank and add some means to deal with the water level fluctuations.

For Raft systems, you still need to make sure you have enough filtration for the fish load and then you can look to Friendlies or UVI numbers to figure out how much plant bed for a particular amount of fish feed.  I don't know those numbers so well but my understanding is that 19 lb of tilapia can be supported in one of their micro systems that has a 300 gallon fish tank and 64 square feet of raft bed.

 

5) yes extra aeration to the raft beds is important for DWC.  Here in the hot south, I recommend at lest some air pumping to the fish tank of any type of system in summer or some means of supplemental aeration because water staying very warm means limited dissolved oxygen and the fish will eat/grow better with ample dissolved oxygen.

 

6 and 7) As to when power out, DWC the raft bed doesn't drain so the plants have plenty of water, either one will keep the plants happy enough for a few hours.  The fish are another story, if heavily stocked some means of battery backup aeration might be needed to keep them alive if the power is gonna be out for more than a few hours.

 

8) The rafts are good for some plants but most will also grow just fine in media and there are many plants that are far more suited to media.  The main benefit of rafts in my experience is gonna be for commercial operations where being able to lift a raft out at one end for harvest then clean up take it to the other end and plant the seedling into the system.

 

Yes combo systems are possible and many people have lately been experimenting with having the fish tank water flow through media beds before going to the rafts to avoid the need for solids removal and separate bio-filtration.

[Pete]

I am designing an experimental system to get myself educated and involved.  I am thinking to have a combo system, deeper media for plants like okra and some 18" deep channels for lettuce etc.,  I would like to try having shrimps in the channels, not sure if they need access to the surface as it will be mostly covered by raft.  That way, I can experiment productivity.  

 

 

[TCLynx]

What kind of shrimp?

 

I'm hopefully about to start growing some cherry shrimp (not big enough to be food for us) if I am successful enough with them, some may become food for catfish.

[Pete]

Good question!  I saw lots of swimming fresh water shrimps or prawns in local Asian supermarket.  Quite big, 2"+, some of them were loaded with eggs.  I have no idea what they are but figure if I can just buy a few pound, quarantine them for a few weeks before releasing to the troughs.  Then hope that they will multiply.   Those are food shrimp, so pretty big.

 

I have purchased those shrimps and live crayfishes for my home aquarium.  They lived for days, some even weeks but eventually all got eaten by predatory fishes.  I have arowana and frontosas, both got big mouths.  

[TCLynx]

Interesting.  Let us know how they go.

[Pete]

My aquaponic is still in the planning stage ...

[David Waite]

Pete my system is a combo or hybrid. My gravel beds  filter for my rafts. I do like the raft concept but honestly rafts are way overrated for the hobbist. You will hear that rafts are more productive or you can plant closer. That is all bull. A hobbist grower doesnt need to produce a head in 25 days and I can tell you my growbeds will compete with rafts in every facet. I also like the gravel for the flexibility of crops to grow. Rafts IMO are great for production of monoculture but a gravel bed for the hobbist grower is way more enjoyable and flexible. In my system my rafts will show deficient nutrients but the gravel wont even though they are  in the same loop. I am not trying to beat up rafts just my opinion on my system. Have fun with it. I designed my system so If I didnt like the raft tanks I can raise my shelf unit and install gravel in about a couple of hours so keep your design flexible.

Pete said:

My aquaponic is still in the planning stage ...