Backyard Aquaponics
A place to discuss aquaponics

Trying to float a raft with an air gap under it is going to be trickier than you expect. Problem is as the plants grow they get heavier and require more of a float but when the plants are small and light you need the raft closer to the water so the plants don't dry out from their roots not touching the water. This is why most operations that use floating rafts have air stones under the rafts.
Some operations use stronger boards that can be suspended above the water level on supports but you still have to make sure the new plants are big enough to reach the water or they will dry out and die and the heavier/stronger supports or boards are often too heavy to lift off the system when full of plants so harvesting and re-planting has to be done in place (probably not a problem for a home system through as you don't want to eat the whole bed of lettuce in one week anyway so you will be harvesting and re-planting only a few plants at a time normally.

G'day Kita, been following your build for a while now, awesome work i have to say! Quick question for you - what are you using as a liner in your DWC? Am in the process of trying to find a suitable and cheap liner for some wicking beds and its more of a struggle than i anticipated!

Cheers
Alan

Thanks Alan, i bought mine from here, quite cheap if it is as good as they say.

http://www.practicalaquaponics.com/shop ... Liner.html

Yeah i just assumed there would be plenty of buoyancy in the pvc but now i think about it i was naive. Am thinking some small soft drink or water bottles might work but don't want to limit grow area too much.

If i can't get the air pocket to work properly its not the end of the world is it? I just run air stones under the beds to provide the oxygen the roots need?

good to keep your options open.

So got 1 of the rafts floating today, using some soft drink bottles . Also brought the duck weed pond home that has been sitting at work for the last few months as want to plumb it in and stop throttling my pump back.
Also discovered my Venturi was restricting my water flow back to the FT so need to work on those a little.

Hey kita, look around the house for some bits and pieces that may resemble the weights of fully grown lettuce (or whatever it is you want to grow) and sit them randomly around the raft. I did this when I was testing my prototype coreflute raft as no one had done it previously. It helped me decide on bracing mine the way I did. A full raft of lettuce can actually be quite heavy and when I grew chard it really tested the integrity out. Food for thought mate (mind the pun)

Oh, and remember, you can also suspend the rafts using the very top edge of the structure, which is basically what I did in the end.


... Ill find a pic

Thanks mate, yeah i have worked out i can lower the level so that the rafts can sit on 1.25l bottles touching the bottom however i am getting good buoyancy out of these smaller ones. I will however heed your advice and run some weight tests.

You could probably even build a PVC frame that goes under the rafts so that you could have the water level touching the rafts when you start the seeds and then lower the water level so the frame would actually act as legs and suspend the raft above the water level by a fraction. I believe this is what they do for the completely passive hydroponics in HI. Basically they have pipes or something down in the water that as the water level drops the rafts will come to rest on the pipes and as the water level drops further an air gap will form under the rafts. This is of course in sterile hydroponic culture. Aquaponics is always going to have bacteria in the water and on all surfaces that will also consume oxygen so some supplemental aeration may still be necessary if the water gets warm.

Mine are on the PVC now, but i have added the bootless for extra buoyancy. As they sit in last pic, 1 has had the bottles fitted and floats with 3/4 inch of the cup suspended in the water which is enough for germination etc and leaves a good air pocket, in addition i am using 8mm corflute which in itself is an 8mm pocket.
The others are just on the PVC, but will have bottles fitted later.
The bottles can be upgraded to larger if need and or have water added to alter buoyancy.

As for air i still intend on fitting a pump and some airstones but with the air pocket i don't have to go too large.

So bit quiet here at work today so got my yardy to make a start on the frame for my strawberry towers.
Make up 2 sets of 2 towers 2.4m high, my biggest problem is plants to fill them, they so damn expensive.
Any tips on the towers? I plan to cut slots then heat and push in the top creating a spot to plant the strawberries in. Haven't decided on clay or gravel, my guess is the clay will probably try to fall out? 20mm blue metal should lock together well but will be bloody heavy. Was planning to fit a bulk head fitting for an overflow at the bottom somewhere to feed back to the sump. Supply will be a feed from one of the sumps via pump to a trickle set up on top. Does anyone have any ideas on flow rates for something like this as it is not flood and or drain.

Hi Kitacooch,

Not to say expanded clay or gravel wont work but I would avoid them both. I have 10 towers with 7 plants in each and I used expanded clay (lighter than gravel but still not light when filled with plants and moist). I have just emptied my towers to replace the plants and media with foam pads (experimenting a bit). I found that the roots of my strawberry plants were black and that ants had a fun time making nests in it as it is not flooded but only dripping through them. I had to take down all the towers and shake them upside down and some were so root bound that it took be perhaps an average of 20 minutes to clean out each tower... if yours are even bigger it could become a REAL PITA.
This season I am using Matala filter mats cut to circular pads which I cut a slit in and insert into each hole.. so far my runners have survived and it has been really hot. With the foam pads I am hoping that I will be able to easily pull the plants out if needed and will reduce the chance of ants (and the aphids that come with them) from making nests. Also as the plant grew (1 year old) I would get the occasional overflow as the root ball became huge and prevented flow.. now with a pad I could pul it out and give it a spray clean if necessary but I think the flow will be much easier through the pad anyhow and not necessary. Also the filter pads will make much beter biological filters than the expanded clay.
Here is a link to me thread and what I have done
viewtopic.php?f=18&t=14429&start=390
Also ignore the filter pads in there as they were experimental and turned out to be too fine so I replaced them with the Blue Matala filter pads which I cut to size with a 89mm hole saw.
Good luck!
PS even with the roots being so gunked up I still got lots of strawberries this year... although much more one one side of the towers where there was morning sun than on the other side

Hi Tom77, thanks for the input mate, how do the Metala Filter Mats stay put? Where did you get them from and how expensive are they?

Got the DW pond plumbed in today and working a treat, just have to get some D Weed to put in there.
Sowed out my floating draft and shooting some seedlings for the grow beds in one of the barely floating rafts.