NFT vs DWC in commercial Aquaponics

[Daniel E Murphy]

Murray Hallam discusses his retrofit in the latest

Aquaponics For Profit

[Daniel E Murphy]

His argument centered around temperature. Larger bodies of water stayed cooler. Also, less plumbing and more sites (area for more plants).


Kobus Jooste said:

I really think it is not a question of one or the other, but what are you trying to achieve? If you go along the route of fancy filters, solids separation and clarification, then I suppose you can slap NFT on as soon as the water comes out of the last fiter stage. As Murray warns though, having only NFT may heat your water up too fast, and make certain crops difficult to grow. If you, like myself, may want to keep all your nutrients inside the AP system in a simple manner, then it is most likely that you may go for a hybrid combination. We have not finished our big system yet, but here are the ratios: Fish tanks and sump - 24% of space, Deep gravel flood and drain filter beds - 16% of space, DWC with the potential for overhead vertical stacks draining into the DWC - 60% of system space. Apart from all the different pro's and con's of different methods, I am weary of too much NFT from a muck build-up and root clogging point of view. Even in my home system, I prefer pipes with a diameter no less than 40 mm for the bulk of water transport, and NFT no shallower than 110 mm. From an economics point of view, I also think you can pack as much or more plants in a raft than in NFT, and I'm possitive that the raft would almost always cost less in terms of infrastructure lay-out and maintenance. Our system, for example, would have 2 banks of gravel draining into 2 rafts each. For a total of 80 meters of DWC length, there will only be about 12 - 15 meters of pipe connecting gravel beds to raft and raft to sump. I make all these assumptions based on material costs and avaiability in South Africa though.

[Daniel E Murphy]

Since I like to grow catfish then maybe this would be a smart alternative for me to raise them in the DWC tanks? Hmm, I think I need to experiment ;P

[David Hart]

Hi Daniel, If you have lots of cats in the DWC troughs, you may end up with too much poo in there. It may become a problem for the roots. With too much stuff building up on them. (?)

I have added 'skeeter fish' to my troughs. But they are pretty little.



Daniel E Murphy said:

Since I like to grow catfish then maybe this would be a smart alternative for me to raise them in the DWC tanks? Hmm, I think I need to experiment ;P

[Daniel E Murphy]

This leads me to another question. Which fish are best in DWC?


David Hart said:

Hi Daniel, If you have lots of cats in the DWC troughs, you may end up with too much poo in there. It may become a problem for the roots. With too much stuff building up on them. (?)

I have added 'skeeter fish' to my troughs. But they are pretty little.



Daniel E Murphy said:

Since I like to grow catfish then maybe this would be a smart alternative for me to raise them in the DWC tanks? Hmm, I think I need to experiment ;P

[Daniel E Murphy]

What I think i learned from your post is that on the ground floor DWC wins and NFT compliments the usage of vertical grow space more effectively.




Kobus Jooste said:

I really think it is not a question of one or the other, but what are you trying to achieve? If you go along the route of fancy filters, solids separation and clarification, then I suppose you can slap NFT on as soon as the water comes out of the last fiter stage. As Murray warns though, having only NFT may heat your water up too fast, and make certain crops difficult to grow. If you, like myself, may want to keep all your nutrients inside the AP system in a simple manner, then it is most likely that you may go for a hybrid combination. We have not finished our big system yet, but here are the ratios: Fish tanks and sump - 24% of space, Deep gravel flood and drain filter beds - 16% of space, DWC with the potential for overhead vertical stacks draining into the DWC - 60% of system space. Apart from all the different pro's and con's of different methods, I am weary of too much NFT from a muck build-up and root clogging point of view. Even in my home system, I prefer pipes with a diameter no less than 40 mm for the bulk of water transport, and NFT no shallower than 110 mm. From an economics point of view, I also think you can pack as much or more plants in a raft than in NFT, and I'm possitive that the raft would almost always cost less in terms of infrastructure lay-out and maintenance. Our system, for example, would have 2 banks of gravel draining into 2 rafts each. For a total of 80 meters of DWC length, there will only be about 12 - 15 meters of pipe connecting gravel beds to raft and raft to sump. I make all these assumptions based on material costs and avaiability in South Africa though.

[David Hart]

Daniel, Personally, I don't know if there is a 'best' fish for dwc or nft or even media beds. Bottom line, the fish are 'just' fertilizer makers' :-)

It seems to be up to the individual, on what you want to raise ( and eat, or not).
Cats seem to be a great choice for you, seeing as how your in N. FL. I know it gets colder there, then just S of Orlando, where I live now. ( I lived in Orangedale for a number of years)

Even here, I'm concerned with the winter being too cold for tilapia. That's why I'm working on an indoor system for the tilapia...and why I just bought another 150 cats, for outside.

[Daniel E Murphy]

When i say best fish for DWC I mean ones that seem to cohabitate with plant roots well. You seem to think catfish would poo it up :)

Circulation I think would be the key there anyway. I have seen videos of raft systems and i think tilapia were raised under the roots. I was curious what others do well.

[TCLynx]

I think most systems keep the fish and plants separate for a few reasons.
1-fish may disturb plant roots if the eat them.
2- too many fish under plants can cause poo build up among the plant roots.
3- Feeding fish under rafts is difficult and the fish food is likely to gunk up the rafts and roots before it can get5- eaten.
4- it is hard to inspect your fish if they are under the rafts in large raft beds (what if there is a dead fish, it would get hard to find!)
5- catching fish would involve disturbing the plants.
6- most raft beds are too shallow for good growth on large fish, deeper tanks would be better for the fish.

Now I can understand putting a few mosquito eating fish in each raft tank but they stay small.

Now I know some people put a small raft over part of their big fish tank and this could sort of work provided the water flow entering the fish tank doesn't splash on the raft and the safety cover over the tank won't smush the plants but I've never had much luck trying this. Fish feed gets splashed up onto the raft.

So, mostly logistics that probably keeps people from raising fish in tanks under rafts. The best fish for it are probably the ones that don't eat lots of plant roots but feeding fish pellets under rafts is problematic and if you are trying to raise the fish under rafts, loads more aeration needs to be added to the water since the surface is covered by rafts and that is where most of the gas exchange in water happens and both the plants and fish will be struggling to share the same water with the same aeration that is restricted so much much more supplemental aeration would be needed.

[Daniel E Murphy]

Good stuff. In this video i watched awhile back I recalled them culturing shrimp in the same system but after rewatching it they, had a central mud pool where the shrimp are raised.

http://www.youtube.com/watch?v=c2z-IdnIGLE&feature=related

I really like this video :)



TCLynx said:

I think most systems keep the fish and plants separate for a few reasons.
1-fish may disturb plant roots if the eat them.
2- too many fish under plants can cause poo build up among the plant roots.
3- Feeding fish under rafts is difficult and the fish food is likely to gunk up the rafts and roots before it can get5- eaten.
4- it is hard to inspect your fish if they are under the rafts in large raft beds (what if there is a dead fish, it would get hard to find!)
5- catching fish would involve disturbing the plants.
6- most raft beds are too shallow for good growth on large fish, deeper tanks would be better for the fish.

Now I can understand putting a few mosquito eating fish in each raft tank but they stay small.

Now I know some people put a small raft over part of their big fish tank and this could sort of work provided the water flow entering the fish tank doesn't splash on the raft and the safety cover over the tank won't smush the plants but I've never had much luck trying this. Fish feed gets splashed up onto the raft.

So, mostly logistics that probably keeps people from raising fish in tanks under rafts. The best fish for it are probably the ones that don't eat lots of plant roots but feeding fish pellets under rafts is problematic and if you are trying to raise the fish under rafts, loads more aeration needs to be added to the water since the surface is covered by rafts and that is where most of the gas exchange in water happens and both the plants and fish will be struggling to share the same water with the same aeration that is restricted so much much more supplemental aeration would be needed.

[TCLynx]

At one point I think Friendlies actually did try culturing the giant tiger prawns under the rafts in their raft beds but they abandoned that since even with all the extra square footage, they could not grow enough of them to make it commercially viable.

[Daniel E Murphy]

I wanted to address each point here and see if it is workable. All of these ideas centers around caging the fish in a partition.

1-fish may disturb plant roots if the eat them.
cages to keep them separate.

2- too many fish under plants can cause poo build up among the plant roots.
are their any circulation patterns that would keep roots sediment free?

3- Feeding fish under rafts is difficult and the fish food is likely to gunk up the rafts and roots before it can get5- eaten.
If each cage had a designated feeding area where food could be somewhat kept from floating off into the rafts?

4- it is hard to inspect your fish if they are under the rafts in large raft beds (what if there is a dead fish, it would get hard to find!)
each cage could have a moving partition to allow you to coral the fish to the feeding zone for inspection or harvest.


5- catching fish would involve disturbing the plants.
See 4

6- most raft beds are too shallow for good growth on large fish, deeper tanks would be better for the fish.
Deeper DWC beds




Also, having a partition in the cage could allow you to separate the large fish from the smaller ones during harvest automatically as the large ones couldn't swim out of the harvest area due to the size of the partition holes. This of course depends on which kind of fish.









Daniel E Murphy said:

Good stuff. In this video i watched awhile back I recalled them culturing shrimp in the same system but after rewatching it they, had a central mud pool where the shrimp are raised.

http://www.youtube.com/watch?v=c2z-IdnIGLE&feature=related

I really like this video :)



TCLynx said:

I think most systems keep the fish and plants separate for a few reasons.
1-fish may disturb plant roots if the eat them.
2- too many fish under plants can cause poo build up among the plant roots.
3- Feeding fish under rafts is difficult and the fish food is likely to gunk up the rafts and roots before it can get5- eaten.
4- it is hard to inspect your fish if they are under the rafts in large raft beds (what if there is a dead fish, it would get hard to find!)
5- catching fish would involve disturbing the plants.
6- most raft beds are too shallow for good growth on large fish, deeper tanks would be better for the fish.

Now I can understand putting a few mosquito eating fish in each raft tank but they stay small.

Now I know some people put a small raft over part of their big fish tank and this could sort of work provided the water flow entering the fish tank doesn't splash on the raft and the safety cover over the tank won't smush the plants but I've never had much luck trying this. Fish feed gets splashed up onto the raft.

So, mostly logistics that probably keeps people from raising fish in tanks under rafts. The best fish for it are probably the ones that don't eat lots of plant roots but feeding fish pellets under rafts is problematic and if you are trying to raise the fish under rafts, loads more aeration needs to be added to the water since the surface is covered by rafts and that is where most of the gas exchange in water happens and both the plants and fish will be struggling to share the same water with the same aeration that is restricted so much much more supplemental aeration would be needed.

[Daniel E Murphy]

>>Looks like you are heading towards a lay-out where you want to max your plant growth space by integrating the fish tanks with rafts.

Indeed I believe many an aquapon thought of this. It would be beneficial potentially saving room of course.

>> If you put in double drains and suck the bottom of your "raft raceways" ends, you now have the solids out, but then what?

I would definitely pump them to gravel beds. I believe that a diverse ecology inspired by a comprehensive aquaponics system comprised of potentially many methodologies where key benefits in each are leveraged in harmony with the rest. Combining DWC fish tanks with gravel beds for biofiltration and additional grow area and NFT seems to allow for maximum space\temperature\cost benefits over any single system. I will let you know how the raft raceways work out. I intend to build a small one for testing purposes then scale up if the system tends to be less of a pain in the butt\more productive then the others :)



Kobus Jooste said:

Looks like you are heading towards a lay-out where you want to max your plant growth space by integrating the fish tanks with rafts. I know of a french-canadian that pulled that off with trout and lettuce, not sure if he is still going. There are a multitude of ways to keep fish wastes and uneaten food from the plant roots, but in the end, the question is going to be: What are you going to do to them to max the mineralization effect you can get from them? You can set up your circulation in the same way that aquaculture raceways operate. You drop your inflow pipes to the floor/side wall corners, with holes in the pipes that directs the flow down the raceway, and toward the centre of the raceway at the same time. It may also help if you slope the raceway floor down towards the centre (straight sides, triangular floor) to force gunk to the centre and down the raceway. If you put in double drains and suck the bottom of your "raft raceways" ends, you now have the solids out, but then what? You will still have to put some filtration method in to mineralize the solids otherwise your nutrient balance will be shot. After you have dealt with all the issues TC Lynx raised and you are attempting to answer, will you have a simpler operation than just tanks, gravel and rafts?

I'm interested in the outcome of your thought pattern - let us know if you are going to build this raft raceway

Daniel E Murphy said:

I wanted to address each point here and see if it is workable. All of these ideas centers around caging the fish in a partition.

1-fish may disturb plant roots if the eat them.
cages to keep them separate.

2- too many fish under plants can cause poo build up among the plant roots.
are their any circulation patterns that would keep roots sediment free?

3- Feeding fish under rafts is difficult and the fish food is likely to gunk up the rafts and roots before it can get5- eaten.
If each cage had a designated feeding area where food could be somewhat kept from floating off into the rafts?

4- it is hard to inspect your fish if they are under the rafts in large raft beds (what if there is a dead fish, it would get hard to find!)
each cage could have a moving partition to allow you to coral the fish to the feeding zone for inspection or harvest.


5- catching fish would involve disturbing the plants.
See 4

6- most raft beds are too shallow for good growth on large fish, deeper tanks would be better for the fish.
Deeper DWC beds




Also, having a partition in the cage could allow you to separate the large fish from the smaller ones during harvest automatically as the large ones couldn't swim out of the harvest area due to the size of the partition holes. This of course depends on which kind of fish.









Daniel E Murphy said:

Good stuff. In this video i watched awhile back I recalled them culturing shrimp in the same system but after rewatching it they, had a central mud pool where the shrimp are raised.

http://www.youtube.com/watch?v=c2z-IdnIGLE&feature=related

I really like this video :)



TCLynx said:

I think most systems keep the fish and plants separate for a few reasons.
1-fish may disturb plant roots if the eat them.
2- too many fish under plants can cause poo build up among the plant roots.
3- Feeding fish under rafts is difficult and the fish food is likely to gunk up the rafts and roots before it can get5- eaten.
4- it is hard to inspect your fish if they are under the rafts in large raft beds (what if there is a dead fish, it would get hard to find!)
5- catching fish would involve disturbing the plants.
6- most raft beds are too shallow for good growth on large fish, deeper tanks would be better for the fish.

Now I can understand putting a few mosquito eating fish in each raft tank but they stay small.

Now I know some people put a small raft over part of their big fish tank and this could sort of work provided the water flow entering the fish tank doesn't splash on the raft and the safety cover over the tank won't smush the plants but I've never had much luck trying this. Fish feed gets splashed up onto the raft.

So, mostly logistics that probably keeps people from raising fish in tanks under rafts. The best fish for it are probably the ones that don't eat lots of plant roots but feeding fish pellets under rafts is problematic and if you are trying to raise the fish under rafts, loads more aeration needs to be added to the water since the surface is covered by rafts and that is where most of the gas exchange in water happens and both the plants and fish will be struggling to share the same water with the same aeration that is restricted so much much more supplemental aeration would be needed.