Things I have learnt since starting hybrid systems.

[Kobus Jooste]

The most important thing is to abandon the single pump lay-out if you want to have media beds and rafts / NFT in a compact space.  In the past, I could drain gravel beds into rafts and then to a sump full of netting.  This kept the water in the system clear and the roots in the rafts looking good.  My new lay-out is NFT above and raft at the same height as the media beds, thus the single supply line I have been using is really too dirty for NFT.  Option 1 is in line filters, and option 2 is small secondary pumps for the NFT.  I'm going for the latter.  A high head low wattage pump will be tossed into the sump as soon as I have installed a internal configuration that settles the solids out prior to it getting to the pump.

 

The second issue I am picking up is that hybrid systems tend to have "just enough" gravel rather than surplus, which means that fines and even intermediate solids seem to stay in the system's water.  I picked this up with the sump retro-fit.  I therefore think that if you are going to run a stacked design with raised beds and lots of media-less culture, you need to find ways to settle out fines the way it is done in raft-type systems, but without discarding it.  We are therefore talking in the direction of mineralization / digestion sections in our AP systems, but not yet solids removal.

[Harold Sukhbir]

Hi Kobus, 

Welcome back from hiatus. Your model conserves lateral space and goes more vertical by design, demanding higher pump pressures. You save one way and pay the other, i guess. Do you think your fish feed can be the cause of higher nutrient as the regular aquaculture feed available to most other AP users? So i see you accepting the 200 plant challenge! Nutrient demanding plants(tomatoes etc) will put a limit on this, so its wise to remove them. Converting the duckweed bins is a better use of space and adds filtration at the same time. Now when you do the commercial trial with super aeration, filtration, added nutrients, and mineralization tanks 

[David Waite]

Kobus my system is just growbeds and rafts at the moment. My towers are off line due to high ph and wanting to plant stawberries in them. My water quality is very high in the raft tanks with a high fish load. Do you think the length of the gravel beds help in that the distance from inflow to siphon is over 6 feet of gravel the water has to travel before it hits the rafts. I am thinking of taking one of my air lines in my raft and lifting clean water to my towers to avoid another pump. Air will lift water no problem and the flow needed is minimal. What do you think.

Kobus Jooste said:

Some new lessons learnt. 

 

If you have relatively small beds, and you plant relatively long-lived crops such as tomato, egg plant, cucumber, pepper, butternut and passion fruit, the beds fill up with root system rather extensively and soon you have a far murkier FT than what you had running leaf crops.  I therefore have come to the conclusion that a person can take the original ratios that we worked with and double them for the GB component if you are going to have long-rotation crops dominating the media beds.  I have presently removed the raft from one of my beds and turned it into a large but temporary filter to try and remove the excess fines in the system that is not ending up in gravel any more.  I will also seriously contemplate cutting back on my fish stocking rates or adding more gravel beds outside the original system footprint. 

[Harold Sukhbir]

Hi David,

Nice !!!!!!!!!!!!!!!!!!  

[David Waite]

Harold ye ol guru what do you think of that concept my friend.

Harold Sukhbir said:

Hi David,

Nice !!!!!!!!!!!!!!!!!!  

[Harold Sukhbir]

Hi David,

I knew you were something special. You got me there! Smaller pumps in vertical steps, we can go higher with less! Great thinking David.

 

[David Waite]

I will build this soon and keep you posted. Gonite.

Harold Sukhbir said:

Hi David,

I knew you were something special. You got me there! Smaller pumps in vertical steps, we can go higher with less! Great thinking David.

 

[Kobus Jooste]

Hi All - sorry for not replying earlier but the time zones and the lazyness you know.......

 

David - I think the air lift will be great if you have redundant capacity - aerated water into towers will be nice for the plants.  I have found that with my small gravel beds, the fines still make it through.  You may not see it in a water sample, but it shows up over time on the roots.  You see it in the sand bed.  The plants coming out of there have pure white roots, while my NFT plants are still happy, but do not have the same root appaerance.

 

Harold - I have a bit of redundancy to work with myself.  At high plant and fish densities, I had a 75 Watt pump always on.  I am now switching to 75 Watt on for 15 minutes and off for 45, and 60 wat on 30 minutes off 30 minutes.  Two pumps will still use less than the one always on.  I will keep an eye on the DO to see if the reduced fish load can cope with the change.  My towers consist of an experiment with timed flow and coir to keep the roots wet for the 30 - 45 minute "off" period.  so far so good.  There will be plenty oxygen available to plants during the "off" period, thus I am still not stressed.  There is lots of oxygen available in the sand bed too.  So with a bit of luck, all the changes I make will not touch the monthly power consumption.

[Kobus Jooste]

Having been experimenting with aquaponic sand grow bed options, I have come to the conclusion that the configuration of wetting that works best for my situation is to irrigate the sand bed over the top of the sand.  I have a pipe grid over the surface of the sand now and the water (at the moment part exess water and part drainage from the compact towers) trickles through the surface of the sand bed.  Below my sand bed the outflow water travels through a NFT tube full of strawberries, and it was just too tricky to set the correct height of flooding when I tried to flood the bed by filling it up to a set overflow point.  Put the water through there too fast and the NFT overflows.  Too slow and the water never rises far enough in the bed to wet the surface sand sufficiently.  Get the overflow a bit wrong and the samller plants get submerged before the pump kicks out.  It would have been a lot simpler to operate the sand bed if it was not stage 2 of a three stage flooding regime (part of my "cube design" philosophy).

 

The simplest compromise in my situation is to irrigate over the surface of the sand and allow the water to build up slow enough not to come pouring out of the NFT.  The plants have responded really nicely to the lower flood levels as well.  One of the things that I am considering now is to have some vermiculite added to the sand.  I have then in my pvc filled towers and they can stay moist for over an hour.  If I can get the "clean line" pump to only come on once an hour during summer, I'd be quite happy.