A Community and Forum For Aquaponic Gardeners

Constant Flood & NFT

The systems I, and 14 others, are building is a combination pea gravel media bed--only a few inches--and NFT. The solids are, for the most part, trapped in the fish tank and smaller particles could be broken down by worms. There is gravel in the fish tank. In the past the school has had success with these systems and I want to put this idea out-there. Has anyone tried this type of mixed system? What should I expect?

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Permalink Reply by Kobus Jooste on September 15, 2011 at 11:51pm

Eric, my main concern is that you are creating a situation where you are confining some of the oxygen depleting reactions to the fish tank. With most of the solids staying there, you are in effect mineralising and nitrifying in the same environment that the fish must respire in - thus three sinks for oxygen. Plus ammonia and nitrite generated inside the fish tank. This can be resolved by supplying a lot of additional aeration in the fish tanks, by having very modest stocking ratios or by trying to move most of the solids out of the system's fish tank. Is leaving the solids in the fish tank a desired outcome or a result of the system configuration? If the water flows out of the fish tank overflow due to pumping back from a sump, you can add a solids lifting overflow (SLO) design to move the solids out, and if you are actively pumping from the fish tank, you can reduce or remove the gravel from the fish tank altogether, and then place the same volume of gravel in a biological filter stage between the fish tank and the pea gravel beds. I would be happier with the latter option. I firmly believe in seperating the different filter stages (it is not a must, but it is what I prefer to do) from the fish or plant "living spaces" as much as possible in order to increase the filter's efficiency and to ensure that the fish and plant environments are as close to optimal as possible.

Permalink Reply by Jonathan Farrand on September 16, 2011 at 10:30am

I have much to add to my system!! This info is spot on for where I am at with aquaponic plumbing and having different elements of filtration. Thanks Kobus!

Permalink Reply by Kobus Jooste on September 16, 2011 at 11:59am

Jonathan, it is a pleasure for me to share what I think are sound concepts in aquaponic functioning, but I do not think that it is the only way to do things. The following pointers, however, is what my thinking is based around:

1) Nitrification bacteria likes to be in close contact with the water supply that contains ammonia, have good oxygen supply and are light sensitive. Coating them in muck is not going to aid nitrification, as you will likely reduce their efficiency. Thus in its purist argument, nitrification is a "second stage" aquaponic process after most of the solids have been dealt with. Muck and plant roots in the end influence the path of water through a bed, and thus, I believe, your nitrification area does not remain the same in a heavily planted gravel bed as it would be in a sump full of floating media of the same dimentions / surface area as the gravel bed.

2) Mineralization is a "first stage" aquaponic process to me, synergistic to worm activity. Both worms and mineralization processes can be housed in the same environment, and a contact area between the media and the water supply is not as critical as in nitrification.

3) pH balancing and gas balance. It is not always the best of ideas to try and add acids or bases or buffers into a fish tank or a filter, thus having a space where you oxygenate / degas and can add your pH buffers is not such a bad idea.

In many home system designs, people try to reduce clutter and components but for the same reason as a fuel injection engin works a bit more efficient than a two stroke, I think that paying that extra bit of attention and infrastructure in setting up multi-stage filtration will pay off.

Jonathan Farrand said:

I have much to add to my system!! This info is spot on for where I am at with aquaponic plumbing and having different elements of filtration. Thanks Kobus!

Permalink Reply by Eric Warwick on September 16, 2011 at 9:48pm

We clean the fish tank, partial water change and vacuum fish waste, about every 60 days. We'll be moderately stocked, so we'll have less trouble, hopefully. Oh yeah, and aeration will be there plus I'll try and integrate duckweed.

Kobus Jooste said:

Eric, my main concern is that you are creating a situation where you are confining some of the oxygen depleting reactions to the fish tank. With most of the solids staying there, you are in effect mineralising and nitrifying in the same environment that the fish must respire in - thus three sinks for oxygen. Plus ammonia and nitrite generated inside the fish tank...

Permalink Reply by Kobus Jooste on September 17, 2011 at 2:17am

Eric, that will work, but are you not selling the concept of aquaponics short by devising a system that needs water changes and bi-monthly cleaning? The core of a stable aquaponic system is one that is allowed to develop stable ecological processes around itself, not one that needs maintenance on a regular basis. Every water change and cleaning disturbes the microbial community and water chemistry of the unit.

Eric Warwick said:

We clean the fish tank, partial water change and vacuum fish waste, about every 60 days. We'll be moderately stocked, so we'll have less trouble, hopefully. Oh yeah, and aeration will be there plus I'll try and integrate duckweed.

Kobus Jooste said:
Eric, my main concern is that you are creating a situation where you are confining some of the oxygen depleting reactions to the fish tank. With most of the solids staying there, you are in effect mineralising and nitrifying in the same environment that the fish must respire in - thus three sinks for oxygen. Plus ammonia and nitrite generated inside the fish tank...

Permalink Reply by Eric Warwick on September 17, 2011 at 12:00pm

It's mostly because of limited space. What do you think would work in terms of reducing solids? Would a crayfish-tilapia polyculture work?

Permalink Reply by Kobus Jooste on September 17, 2011 at 12:57pm

Do you have a schematic of your planned system? I understand that space is limited but without knowledge of what goes where and if you have constant height in most of it or a number of different heights with a sump included would help me in commenting on the amount of first stage filtration that you are planning.

Permalink Reply by Eric Warwick on September 17, 2011 at 1:39pm

This is the drawing about what is known for the filtration aspect. I don't know how the NFT will be added. The fish tank (FT) is a 40gallon or 50gallon barrel. The height variation in the design is to show it's slanted. The system will be built by 15 people in my bio/chem class--most of which recently learned what aquaponics is one week ago or less. Anyways I hope my bad drawing skills don't get in the way.

Permalink Reply by Kobus Jooste on September 17, 2011 at 3:13pm

Without knowing if the pump is in the borttom of the barrel (Which should get a lot of the solids out) or if there is some sort of sump pumping back into the barrel (which would keep the solids in the barrel if you are not using a SLO), my concern is that the water goes from ft to shallow gravel to NFT. The NFT is not going to operate at best if a lot of suspended material makes it in there, and as your gravel beds are only a few inches deep, you do not want to hit it with too much solids as it will not be able to handle it. You may also run into nitrification problems but I'm not sure as I do not have the dimentions of the pea gravel bed. I would have a fine screen between the pea gravel and the NFT to ensure clear water delivery (may have to be cleaned every couple of days) and I will try to fit a deeper gravel structure to act as a mineralisation / mechanical filter between the FT and the pea gravel bed. It does not have to be big - 10 - 15 gal capacity with a bottom drain to make cleaning a bit easier. This way you do not have to do frequent water changes, but monitor the state of the water and clean the first stage filter only if needed.

Permalink Reply by Eric Warwick on September 17, 2011 at 4:20pm

The pump is probably going to be at the bottom.

Kobus Jooste said:

Without knowing if the pump is in the borttom of the barrel...

Permalink Reply by Eric Warwick on September 17, 2011 at 4:26pm

@Kobus I'll direct my teacher to this thread. I'll try and get more information.

Permalink Reply by Eric Warwick on October 9, 2011 at 6:17pm

Update: The system is more like a nft media combination in the sense that it's similar to nft and it's media. However no specific NFT system is added. I'll copy this over to the media based discussions since it's not really a mixed system. The diagram I shared is how the system looks.