bio-media on the floor of a raft system

[Daniel Gunloche]

Hello all,

I'm sure this has been discussed before, but I can't seem to find anything on it.  Could gravel media (let's say 8" deep) be placed on the floor of a raft system for biofiltration purposes? Would there be enough aeration for it to function properly?  It sure seems like this would provide a whole lot of surface area for needed biofiltration in this type of system.

 

Thanks,  Dan

[TCLynx]

I think in most situations it will likely cause more issues than it solves.

 

Aeration would be the primary issue.  And then solids (in the form of fish poo and plant roots and leaves being lodged in the media breaking down and robbing oxygen would also be a issue to look at.)

 

Space and the roots tangling into the media making floating the rafts down the line without damaging the roots would also be an issue.  Most raft beds are about 12 inches deep and probably 10 inches of water depth so that would only leave a very small amount of water depth for the plant roots before they are growing into the gravel.  Now if you are not moving the rafts down the line like a conveyor, the plants will probably not mind this so long as you are some how providing really oxygen saturated water at a good flow through the bed. 

 

But at that point, why not just fill the bed all the way up with gravel and run a constant flow/flood media bed and skip the expense of additional air stones, rafts, net pots and the extra planting time into the net pots.

 

If you really want raft, then you can get lots of filtration simply by adding a barrel of media as an upwelling filter with aeration before the beds and if you have a settling tank you may not have to clean the filter much.  Then you are left with easy to deal with open rafts beds that you can more easily inspect the air stones and float the plants along the line and if you do start to get much debris in the bottom of the raft bed it will be far easier to clean out without gravel or other media in the way.

[Harold Sukhbir]

Hi Daniel,

If you really wanted to design a raft trough with 8 " of media it could be done. The raft construction would have to have very strong sides, most probably concrete sides(or smaller lined wood box troughs) , the water depth 12" plus 8 " media equals at least 20" deep, and sufficient under gravel aeration. Your ratios for fish could be higher than the standard for raft(1/3 lbs fish per sq.ft.raft), as you are creating more nitrification surface area, but not high enough to cause clogging of the media. This set up will cost more than the standard to make and operate and more construction time is involved. IMO i like the last suggestion by TC, adding remote media.

[Daniel Gunloche]

Thanks guys,  I would really like to do a raft conveyer type system, but I see you are right again, it would be simpler just to do the filtration elsewhere, I know I am again thinking outside the box here...  but for strawberries,.. So it would be a conveyer that would move in a more constant repeatable cycle.  I also know strawberries are a bit iffy, but has anyone successfully done strawberries in a raft system?  Now my thinking is that if strawberries were on a conveyer, that the greenhouse could have a very low ceiling height, maybe even just a few feet, and cycle the rafts into a small full height room for the processing.  I would think a heated troughs would be all that is needed even in winter for such a low volume of airspace. I suppose the trough areas would still need to be accessable in case of possable raft jambs or maintenance, do you need to access the trough areas very frequently?

Thanks again,

Dan

Harold Sukhbir said:

Hi Daniel,

If you really wanted to design a raft trough with 8 " of media it could be done. The raft construction would have to have very strong sides, most probably concrete sides(or smaller lined wood box troughs) , the water depth 12" plus 8 " media equals at least 20" deep, and sufficient under gravel aeration. Your ratios for fish could be higher than the standard for raft(1/3 lbs fish per sq.ft.raft), as you are creating more nitrification surface area, but not high enough to cause clogging of the media. This set up will cost more than the standard to make and operate and more construction time is involved. IMO i like the last suggestion by TC, adding remote media.

[TCLynx]

Keep in mind that if you are heating the water and not the air in a greenhouse system in a really cold season/climate you will have some major condensation and perhaps frosting issues since the warm water will evaporate quickly into the cold air and then condense quickly onto the colder surfaces.  In such a situation I fear strawberries may have some major fungal issues too and berries laying on the rafts might also have a greater tendency to rot.

 

This is why many people prefer towers or NFT for strawberries since the berries are more likely to be hanging free instead of resting on something.

[Daniel Gunloche]

Yes - and that is a good reminder as to why I have berries in NFT channels with a ridged lid now, The hanging part kinda slipped my mind when I thought about the rafts....  Do you know if strawberry roots do OK in a raft type system?  I have a few in a raft right now just experimenting, but they have only been there a few days now.  Thanks  Dan

TCLynx said:

Keep in mind that if you are heating the water and not the air in a greenhouse system in a really cold season/climate you will have some major condensation and perhaps frosting issues since the warm water will evaporate quickly into the cold air and then condense quickly onto the colder surfaces.  In such a situation I fear strawberries may have some major fungal issues too and berries laying on the rafts might also have a greater tendency to rot.

 

This is why many people prefer towers or NFT for strawberries since the berries are more likely to be hanging free instead of resting on something.

[TCLynx]

Never tried strawberries in rafts or nft myself.  Strawberries are rather resentful of having their crowns stay too wet so you would at least need to make sure the rafts floated high to keep them from water logging.

[Daniel Gunloche]

Thanks TCLynx,  You have made it clear that this really wouldn't be the way to go. I'll stick with something similar to what I have now.  As I had mentioned before in a previous thread, right now I have 4" PVC pipe with a lengthwise 2-1/2" wide slot cut out of the top of the pipe, and filled with 3/4" gravel,  The channels are set level and I am flooding and draining these to 1" from the top of the gravel to keep crowns dry etc.. There are 1/2" fill/drain lines entering the bottom of this pipe channel every 5' with a simple rolled up piece window screen standing in each fill/drain line to keep the debris out of the fill line   Seems to be working great so far, with good airspace for the hanging berries, good aeration to the roots,and minimal weight. I have deep bio media beds elsewhere as well.  I have just switched over to AP from hydro and the system is still cycling and looking good, I am excited!  Only time will tell if 4" is enough root space, maybe 6" pipe would be better.  Any thoughts about all this?  I value your input, and thanks for steering me away from the raft tangent, I could have wasted a lot of time and effort on that experiment.  Thanks  Dan

TCLynx said:

Never tried strawberries in rafts or nft myself.  Strawberries are rather resentful of having their crowns stay too wet so you would at least need to make sure the rafts floated high to keep them from water logging.

[Harold Sukhbir]

Hi Daniel,

If you really want to grow strawberries take a look here

http://aquaponicscommunity.com/photo/strawberry-towers?context=user

[TCLynx]

Having not had a good pH range for strawberries in my big system, I can't comment much on them.  I've used 4" pipe for NFT and occasionally I have to root prune the basil if it gets out of hand.

 

In larger media beds the timed flood and drain seems to have less problems with roots and slime clogging but you do need to access the drain lines occasionally to clean out roots but you probably know that from hydro too.

 

Media filled pipes are likely to experience root clogging if run constant flow but I don't know about with the flood and drain.  going up from 4 to 6 inch pipe is probably not going to completely solve the problem either.  Re planting and cleaning out the pipes occasionally may be inevitable.

[Daniel Gunloche]

Harold,  I have looked at Nate's berries - very interesting.  But I am wanting to go with a very low initial cost.  I figure pipe or gutter and gravel would still be most cost effective.  I am also dead-set on making some kind of conveyer system that moves 4' wide racks (or groups) of channels thru one climate controlled (human occupied) processing area.  So the greenhouse would be wall-to-wall plants and the ceiling could possibly be only 18" or so above the plants, and these channel racks would be conveyered out into the processing area - that is why I was thinking rafts, but no such luck...  I would think that wall-to-wall plants combined with extremely low ceiling height in such a system would be the most energy efficient. The processing area that the channel racks pass over could also be a pit so berries might be harvested from underneath. -  Well I am always outside the box - but right now I guess AP is outside the box too.  Thanks  Dan

Harold Sukhbir said:

Hi Daniel,

If you really want to grow strawberries take a look here

http://aquaponicscommunity.com/photo/strawberry-towers?context=user

[Anthony Leotta]

I grew strawberries this winter in standard cheap hanging pots.  Filled the pots with cococoir and added a drip line over the top that turned on for 10 minutes every 3 hours. Water drained out the bottom of the pots and back into the fish tank.

[Daniel Gunloche]

Very cool - looks like several plants per pot?  Isn't 10 minutes every three hours a bit low?  I thought AP requires the nutes to be delivered more often because of the low level of nutrients in the solution.  This is interesting because maybe I can cut my cycles back to keep the roots a little less saturated...   Dan

Anthony Leotta said:

I grew strawberries this winter in standard cheap hanging pots.  Filled the pots with cococoir and added a drip line over the top that turned on for 10 minutes every 3 hours. Water drained out the bottom of the pots and back into the fish tank.