Flood and Drain Gravel Grow Beds

[GaryD]

Hi,

It would be no secret to most people who read this forum (and Murray's forum) that we disagree about whether solid wastes should be removed from an aquaponics system.

In a very recent post on his forum, Murray talks about digging up a grow bed in his Homestead system. He has consistently argued that this system is (after nearly four years of operation) still functioning well.

My question is......."If this system has worked so well, why has it killed so many hundreds of fish?"

Gary

[nick]

i was reading the posts at BYAP as well as following Murray's forum and I am disturbed by the thought that water quality as a result of not removing solids is being touted as the primary killer in Aquaponics.

In my memory and personal experience, the number one killer of fish is lack of air.
And also from memory if someone asked me what had been the second most killer of fish it would be a failure to cycle systems.

I can not honestly remember any one person saying help my bed is full of fish waste and my fish are dying. This seems like a statement made to discredit the major aquaponics systems that are already in the market.

Where did it come from?

Also the continual flow system that you tout seems like its only benefit is to make systems twice as expensive to set up than when using gravel. Why is there no use of continual flow in pure hydroponics, there is flood and drain, there is NFT and there is deep flow using air pumps to increase the oxygen in these tanks. So where did continual flow in media come from. I know you will say that Aquaponics is not Hydroponics but the same techniques for aquaponics all came from hydroponics in one form or another.

Well that is my gripe and I eagerly await your reply,
Nick

[GaryD]

Hi Nick,

i was reading the posts at BYAP as well as following Murray's forum and I am disturbed by the thought that water quality as a result of not removing solids is being touted as the primary killer in Aquaponics.

In my memory and personal experience, the number one killer of fish is lack of air. And also from memory if someone asked me what had been the second most killer of fish it would be a failure to cycle systems.

You're correct.......the lack of oxygen is the biggest single killer of fish in small-scale aquaponics systems.

Low dissolved oxygen levels can be the consequence of equipment failure......and they can just as easily result from complications arising from a build up of solid wastes......which I describe in detail here.

Also the continual flow system that you tout seems like its only benefit is to make systems twice as expensive to set up than when using gravel.

How can continuous flow be more expensive when you are spared the cost of the autosyphons, timers and/or float switches. Although I use clay pebbles in my systems, you can use continuous flow (surface) with gravel.......and it's still cheaper. And, based on my experience, there's no noticeable difference in the plant growth.

Why is there no use of continual flow in pure hydroponics, there is flood and drain, there is NFT and there is deep flow using air pumps to increase the oxygen in these tanks. So where did continual flow in media come from.

There is continuous flow in hydroponics. In fact, in some quarters it's more common than flood and drain. I first saw it used succcessfuly by Martin O'Dee in some of the aquaponics systems he established. He subsequently converted several other systems. Impressed by the simplicity and reliability (and the plant growth) associated with continous flow, I also converted my 4 tank system.

I know you will say that Aquaponics is not Hydroponics but the same techniques for aquaponics all came from hydroponics in one form or another.

I'm not going to say anything of the sort. I agree with you.

Nick, high solids loadings can lead to fishkills as I've demonstrated.....but that's not the only issue. Having to reduce feeding to offset deteriorating water quality is counter-productive.

It is much sounder (from a financial standpoint) to design a system to keep the water in optimum condition so that it can cope with higher feeding rates (and higher stocking densities) - so that the fish grow faster and reach eating (or marketing) size earlier.

Gary

[Castaway]

My question is......."If this system has worked so well, why has it killed so many hundreds of fish?"

Whose fish are you talking about Gary? Yours?! I have one of Murray's systems now for 9 months and I haven't lost a single fish. Not one. I have grown a lot of vegetables without incident. The system that Murray has built has worked flawlessly. So I don't understand what or whose fish your are talking about. Please explain your gripe.

If your fish are dying, please Gary, raise a question at http://www.aquaponics.net.au/hq/ There are many kind people there who could help you.

We all need help sometimes...

[GaryD]

Hi Castaway,

I have had many dead fish.......they usually came with salad and a few chips.......and I enjoyed just about every one of them.

I've also had the occasional mishap.....from which I've learned valuable lessons.

Congratulations on raising your fish to this stage.......but Murray hasn't been anywhere near as successful with his large system. It has killed many hundreds of fish.

Did you have a technical issue that you wanted to raise or debate?

Gary

[nick]

dear Gary,
How can you compare the cost of 500l of clay balls to a $9 timer, the use of clay must almost double the cost of a setup. I have read yours and Martins comment about the use of continual flow and in one of you writings it says that clay balls must be used as they alone are porous enough to draw up water from the lower levels where the water is.

Also can you point me towards the locations where it mentions continual flow utilising media instead of say NFT or DWC I have gone to the great mediator of all things knowledgable (wikipedia) and there is mention of continual flow but it just as soon moves straight to an NFT example.

In the Mythconceptions blog you have written you make comment on autotrphics and heterotrophic bacteria and how one grows fast and works on the solid waste and the other slowly and works on the ammonia. But my question for you is that if you are having the effects of the fast and bad than you most likely are already killing your fish with ammonia from there gills as the system is likely not cycled.

My point is that the heterotrophic bacteria will have nothing to feed on until after the autotrophic bacteria are well and truly established. And you point out that if the heterotrophic bacteria are working in large numbers then the system will be leaning towards alkaline and this makes the ammonia more dangerous, but ir your system is structured like mine than all of your wastes are at one end and by the time the water gets back to my fish it will have gone back past the autotrophic bacteria that are well and truly established if my fish are producing enough partially clog the system.

I think you make some valid points but I think the ultimate point is that there are lots and lots of systems using flood and drain with either autosiphons or timers. Most of these people stick to ratios that are quoted to them from people who have as much and more experience than you and I and they grow both fish and plants well. When they follow the rules set out for them by the suppliers they grow plants in such a simple way that it seems riduculous.

You seem to be recomplicating an issue that was simplified by a number of people to make it as easy as possible for people who have no previous experience. You are aiming to maximise fish production at the cost of simplicity. I feel that you may have lost fish because you were running one tank (900l or 1250L) to one 585l growbed. In the commonly held ratio terms you were running a 2:1 tank to bed ration where as the recommendations for safe and easy aquaponics is 1:2 tank to bed ratio. This could have been the reason why you did not see the success and ease that you were aiming for. But Gary I do recognise and remember that you have always been trying to push the ratios and break new ground.

The beauty of fingerlings is that they produce small amounts of waste and then they grow and produce more waste as they grow till the time when they are harvested, when they are producing lots of solid and dissolved waste. this waste goes to the beds and is broken down while you restock with fingerlings and adds to the nutrients available to the plants while the fish production is low.

On the case of murray and his fish deaths, he has definitely killed a lot of fish and I think to his credit he has always owned up to them. But I do not think that a large number of them were from bed waste build ups. He lost an original lot to the addition of excess thrive in a bid to enhance the cycling of one of his systems, ha has also lost a group of murray cod I believe from an air pump failure ( something I have myself experienced) so quoting murray as someone who has lost a lot of fish due to poor product design is a bit of false statistics. It would be fairer to quote a fish lost to those eaten ratio.

Any way some of that will make sense and some of it will be confronting but I feel you will enjoy it all anyway,
Nick

[GaryD]

Hi Nick,

How can you compare the cost of 500l of clay balls to a $9 timer, the use of clay must almost double the cost of a setup. I have read yours and Martins comment about the use of continual flow and in one of you writings it says that clay balls must be used as they alone are porous enough to draw up water from the lower levels where the water is.

There are two types of continuous flow media-based systems. One type (surface watering) features a watering grid and seedlings are planted adjacent to the holes so that they are always exposed to water. This type of continuous flow system can use gravel or clay pebbles.

The other type (subsurface watering) is where the water runs along the bottom of the grow bed at a pre-determined depth. The water hydrates the clay pebbles so that the plant roots are kept moist but not waterlogged.

Both types work well.

Also can you point me towards the locations where it mentions continual flow utilising media instead of say NFT or DWC I have gone to the great mediator of all things knowledgable (wikipedia) and there is mention of continual flow but it just as soon moves straight to an NFT example.

Continuous flow was commonly used to grow lettuce or herbs in PVC pipe (or gutter sections) filled with gravel. It also features prominently wherever satellite pots are used. John Mason makes mention of sub-surface irrigation in his book Commercial Hydroponics. (Page 58 and a diagram appears on Page 24).

J. Sholto Douglas described sub-surface irrigation continuous flow beds in his book Hydroponics - The Bengal System (first published in 1951).

In the Mythconceptions blog you have written you make comment on autotrphics and heterotrophic bacteria and how one grows fast and works on the solid waste and the other slowly and works on the ammonia. But my question for you is that if you are having the effects of the fast and bad than you most likely are already killing your fish with ammonia from there gills as the system is likely not cycled.

Fish will die much more quickly from lack of oxygen than from increasing ammonia levels.

My point is that the heterotrophic bacteria will have nothing to feed on until after the autotrophic bacteria are well and truly established. And you point out that if the heterotrophic bacteria are working in large numbers then the system will be leaning towards alkaline and this makes the ammonia more dangerous, but ir your system is structured like mine than all of your wastes are at one end and by the time the water gets back to my fish it will have gone back past the autotrophic bacteria that are well and truly established if my fish are producing enough partially clog the system.

Bacteria are not confined to the media - up to 70% of the bacteria in a system may be in the water.

I think you make some valid points but I think the ultimate point is that there are lots and lots of systems using flood and drain with either autosiphons or timers. Most of these people stick to ratios that are quoted to them from people who have as much and more experience than you and I and they grow both fish and plants well. When they follow the rules set out for them by the suppliers they grow plants in such a simple way that it seems riduculous.

I don't deny that autosyphons, timers and float switches work - I've used all of them. I have stated that, for sheer simplicity and reliability, I now prefer continuous flow.

You seem to be recomplicating an issue that was simplified by a number of people to make it as easy as possible for people who have no previous experience. You are aiming to maximise fish production at the cost of simplicity.

What I'm trying to do is avoid people becoming disenchanted because of system failures that were precipitated by poor (or simplistic) advice.

I feel that you may have lost fish because you were running one tank (900l or 1250L) to one 585l growbed. In the commonly held ratio terms you were running a 2:1 tank to bed ration where as the recommendations for safe and easy aquaponics is 1:2 tank to bed ratio. This could have been the reason why you did not see the success and ease that you were aiming for. But Gary I do recognise and remember that you have always been trying to push the ratios and break new ground.

The fact is that we have lost relatively few fish and the one major fish kill that I did experience (where we lost about twenty over two days) was for reasons that we never correctly identified.

We also lost 150 out of 200 Murray cod (at the rate of 2 - 3 per week) over a period of over a year. When we asked someone of considerable experience of rearing these fish, his response was, "That's Murray cod for you." I believe (based on our experience of them) that they had a requirement for water of higher quality than that afforded by the standard flood and drain aquaponics system.

I don't have any anxieties about my 4 tank system......it was largely premised upon my microFish Farm design.....and as long as I wanted to run jade perch, that system would still do it very comfortably at stocking rates that I was comfortable with.

It extended my understanding of various aspects of aquaponics - particularly the behaviour of fish solid wastes in a media-based system.

The things we learned from the 4 tank system led us to The Queenslander.

The beauty of fingerlings is that they produce small amounts of waste and then they grow and produce more waste as they grow till the time when they are harvested, when they are producing lots of solid and dissolved waste. this waste goes to the beds and is broken down while you restock with fingerlings and adds to the nutrients available to the plants while the fish production is low.

There will always be some sediment that remains after the fish waste has been processed for (and used by) the plants.

On the case of murray and his fish deaths, he has definitely killed a lot of fish and I think to his credit he has always owned up to them. But I do not think that a large number of them were from bed waste build ups. He lost an original lot to the addition of excess thrive in a bid to enhance the cycling of one of his systems, ha has also lost a group of murray cod I believe from an air pump failure ( something I have myself experienced) so quoting murray as someone who has lost a lot of fish due to poor product design is a bit of false statistics. It would be fairer to quote a fish lost to those eaten ratio.

I have no issue with the fact that Murray has owned up to his fishkills. I do, however, think that he needs to take a less dogmatic line.

I haven't criticised Murray's product.....tanks are tanks and grow beds are grow beds. I've purchased many items of equipment from Murray. My argument is not with the equipment but rather with the standard flood and drain aquaponics configuration. I believe that useful improvements can be made to that arrangement.....and I'm happy to debate the merits (or otherwise) of my ideas. I'm at a loss to understand why some people find that so threatening.

Murray continues to promote the grow beds linked to his big system as being a model of aquaponic excellence. If you take account of the fish mortality question that doesn't quite stack up. Once again, it's not the physical components that are at issue and it's not personal; it's the configuration. I think any similar system managed in the same way would eventually produce the same results.

Any way some of that will make sense and some of it will be confronting but I feel you will enjoy it all anyway,

I don't find your comments confronting.....and I always enjoy a frank but courteous exchange of views. I wish more people were able to demonstrate a similar skill.

Gary

[David McPherson]

I have gravel growbeds operating on a flood and drain system for the last 2 years Recently I stripped all the vegitation out of one to replant it and decided to dig to bottom of trough to see what was there nothing except big fat earth worms I have killed a few fish in the time it has been operating all by bumping plugs and cutting off power to system etc ie lack of oxygen Now I have to wory about my fish dying from dirty water Can anybody tell me what signs and symptons to look out with fish dying from dirty water David

[GaryD]

Hi David,

Fish don't usually die from 'dirty' water as such.

Before I respond to your question, can you update us on the details of your system....including:

• Fish tank volume
• Fish species
• Total grow bed volume

Nice to hear from you again.

Gary

[Ravnis]

Is solids removal necessary? You be the judge.

I have had the good fortune to experience equipment failure while I am still in the beginning stages of aquaponics.

The first time the pump went out, and it was 6 hours before I got it working again. I checked the ammonia level and it had risen to 8.0. The pump workings were covered with sludge and I feel that this contributed to the pump failure.

I added a swimming pool filter I had used for a 5000 gallon pool and filtered out the solids threw mechanical filtration. I also added a sedimentation tank and scooped out the solids accumulation into my BSF biopod on a weekly basis.

The second time I had a pump go out, I was at work and a friend checked it for me and saw that it went out. He had tried to call me but I did not have a phone on me at work. So I did not find out about the failure and get it fixed for at least 12 hours, maybe more. I checked the ammonia level and it was only 2.0. These failures were 3 months apart and I was in the middle of replanting growbeds with the second failure, while the first had fully established and fruiting plants. The fish had grown considerbly so despite a higher fish load the ammonia levels were relatively lower. The only difference I can account for the difference in ammonia levels is the solids removal.

Would it have made a difference if the pumps had never failed, I don't know, but during a catastrophe it made a recordable difference in the ammonia levels.

I have read on aquaculture sites as well as been told by a person that specializes in aquaculture that suspended solids can interfere with gill function in fish.

My observation.