Water Turnover

[GaryD]

Hi,

Crusty has continued his scrutiny of my blog (which I appreciate) and, in response to Mythconception #8 - Water Turnover, he offers the following:

Actually, it is turning over the entire system water per hour NOT the fish tank water volume. Thinking otherwise is a little dangerous. It is an accurate assessment if the “myth” is actually turning the TANK over per hour.

What I was suggesting (and wrote) was that the frequency with which the contents of a fish tank must be turned over are driven by circumstance rather than simplistic formula.

I then went on to say that some of the factors that impact the pumping rate include:

• the type of bio-filtration in use
• the pumping regime – flood and drain or continuous
• the aeration provisions
• whether sedimentary and suspended solids are removed.
• the amount of fish biomass.
• fish species
• water temperature

The list is not exhaustive.....and should include consideration of feed type and other variables.

As we know the hydroponic plant volume of most systems is bigger than the aquaculture fish volume. For example, if you have 10,000 aquaculture and 20,000 liter raft system and use this “turn the fish tank over once per hour” which applies a flow rate of 10,000 per hour in fact will only turn the fish tank over once every three hours. Flow rate guideline would be a minimum of 30,000 liters per hour..

From a basic standpoint turning the water over in the entire system (including pipework) once per hour is quite a safe guideline. I don’t think it is very useful to anyone to suggest something is a “myth” without providing an example of the formula (which there is several) or an alternate solution for people to make their own calculations and come to their own conclusions. However, to suggest the calculations required to design the flow rate of a system is complicated is an accurate summary.

The main considerations for flow rate are TAN and Solids removal which are dictated by the feed used. Yes, there are other equations related to feed to calculate these two. But it is the TAN and Solids removal that will dictate the flow rate.

TAN is directly to the protein level in feed and fish excretion.
The solids generated is related to feed rate.
The feed rate is related to feed conversion ratio and specific growth rate.
These are related to metabolic rate.
and so on we go….

Considering the current aquaponic methods rely on the grow beds as their bio filter and solids filter the TAN and solids equations become rather pointless. In a backyard environment without the use of adequate filtration a general rule of thumb can only be used.

The use of filtration is another conversation all together related to your bio mass. Perhaps Gary would like to do a little myth busting on that issue?

Oxygen is another equation all together and something majority of people not involved in its use will not know and it is quite complicated. For example calculating the oxygen consumption is just like the above two consideration and it related to the feed used. But if you are looking for a starting point to play with is an average of 0.9kg of O2 is generated with diffusers per killowatt/hour. If you know what your fish demand is and your bio demand is you can start to calculate the amount of air you need to some degree. Confused yet?

The good news is there’s another one of those “mythical numbers” that are used in general terms which result in sufficient aeration with the use of diffusers. Even at densities up to 40kg/m3. I hesitate to provide this as it may be viewed as a snake oil salesman’s magical solution.

So, suggesting a turn over rate of the ENTIRE SYSTEM WATER ONCE PER HOUR is an adequate MINIMUM to work from.

I have a quote that probably covers this.....

"I am not sure how suggesting that generalised advise on water turnover is worthless and then offering generalised advise on water turnover is helpful. Further, suggesting people turn over their entire system volume without knowing what type of system or filtration (or all of the other variables involved) they have is downright careless.

......and then I should probably go to say.....

As much as I enjoy people trying to make a difference, I prefer that the information being provided is pertinent and accurate. If not it simply contributes to the confusion and ignorance surrounding aquaponics."

Most of the systems that most APHQ members would typically deal with would be far smaller than 30,000 litres.....and would usually be media-based flood and drain units. Since such systems are usually lacking in adequate mechanical and biological filtration, they would be usually be much more hostile environments than the raft system you've used as an example. This may mean that even changing the entire system once per hour may not be enough.

At the end of the day, keeping fish alive and healthy in a recirculating aquaculture (and aquaponics) system depends on the ability of the system to convert ammonia to nitrates, to rid itself of harmful gases (like carbon dioxide)….and to meet the oxygen needs of the fish.

Most backyard fish farmers will opt for a simplistic formula and risk getting caught out because it fails to address the variables adequately. Those who attempt a complex formula run the risk of getting the math wrong.

Conducting water tests (and responding to them in a timely manner) is really the only way you're going to determine if your pumping rate is adequate.

It is a good idea to oversize your pump in these backyard systems so the flow rate can be increased as needed (can always choke pumps back).

I agree that having more pump than you need is a good idea. Rather than throttle the pump, however, I'd recommend fitting a bypass and using the spare capacity to move water around. It's better for the pump and at least you get enhanced aeration for the extra money that it costs to run the larger pump.

Two smaller pumps are a better idea so if one breaks down, you have at least some flow rate until you get a new one. The chances of them both breaking down at the same time are rare. The alternative is to have two of the same size pump, plumbed in line in case one breaks. Then you can alternate pump loads between the two.

While this is something that I sometimes recommend, the important thing is to ensure that there's a back up system of some sort in place.

Gary

[Crusty]

I have a quote that probably covers this.....

"I am not sure how suggesting that generalised advise on water turnover is worthless and then offering generalised advise on water turnover is helpful. Further, suggesting people turn over their entire system volume without knowing what type of system or filtration (or all of the other variables involved) they have is downright careless.

......and then I should probably go to say.....

As much as I enjoy people trying to make a difference, I prefer that the information being provided is pertinent and accurate. If not it simply contributes to the confusion and ignorance surrounding aquaponics."

Most of the systems that most APHQ members would typically deal with would be far smaller than 30,000 litres.....and would usually be media-based flood and drain units. Since such systems are usually lacking in adequate mechanical and biological filtration, they would be usually be much more hostile environments than the raft system you've used as an example. This may mean that even changing the entire system once per hour may not be enough.

Ok permit me to put it another way. We are talking about flow rates alone and assume you have some form of filtration. If you have gravel grow beds attached to your fish tanks, turning over the system water once per hour is a good minimum to start with not withholding the use of some serious formula to calculate accurately what you need. The 10kL:20kL example can be scaled down to suggest that if members are not running an aquaculture system alone (which we are not talking about) they will have some form of grow beds acting as a bio filter to some extent 1:2 (then we start up the argument of ratio advice).

Yes we are making a great many assumptions but unless everyone wants to send me the details of their system, everyone needs a guideline to start from or they will have to learn some engineering math and work it out themselves. Which I doubt will be the case. The alternative, is they take the advise of others that will lead to problems, or you can kill fish and learn from that.

I use that guideline to start the design of aquaculture farms, with filtration. Then the filtration is worked up from there and has only needed be changed for some species of fish. For example, salmon require strong velocities because when they swim in the current it is like body building for them, if they are in still water they do not put on weight, they lay down fat. Further, the velocity in a tank must not be too high (approx. 0.3m/s max).

Even further still, your plants will not like the kind of flow rates your fish need so those using filtration will be diverting the flow back to the tank in an attempt to reduce the flow rate to the plants. If you do not have filtration, you can only slow down the entire system. Which in turn is worse than speeding it up.

Considering I use this basic guideline for commercial aquaculture, it will be overkill for low density back yardies. That is why I can confidently offer it as a safe starting point. If you have inadequate filtration (eg not enough grow beds or dirty ones) increasing or decreasing that flow rate will have little to no effect on your TAN removal capacity. Bio filters do not work that way.

So, I suggest you start with this flow rate and as with any system the first month should consist of daily water testing. The first 10 to 14 days are your danger zone where only heterotrophs are present converting organic waste (poop and wasted feed) to ammonia. After 10 to 14 days and if you have sufficient amount of ammonia your nitrosomanas will be present enough to oxidize the ammonia to nitrite. The next 2 to 4 weeks is another danger zone for the nitrobacter (these guys are inhibited by ammonia) to take a hold and oxidize your nitrite to nitrate. During this 4 to 6 weeks you will be required to "manage" the water. If you are outside that time and can not get stability, your filter is insufficient. No manner of water flow will change that.

Perhaps Gary, you would like me to offer the formula for calculating if your bio filter (grow bed) is adequate, before you get the fish? I thought this would have been in your book mate...

Because the formulas are complicated I will give you a few examples. This calculation has a very large safety net and many assumptions.

Assumptions made:

1. Surface area of expanded clay of 90m2/m3 (can be 2500 but when those pores are blocked with organics that number is drastically reduced to 90m2/m3 - always use worst case for biofilters as the activated surface area will differ from the actual surface area often lower.)
2. Feed protein 35% (majority of native fish feeds are around this mark though carnivore (barra) feeds are considerably higher - Also younger fish tend to have higher protein diets)
3. Feed rate 2% (this varies with the fish age but generally at the end harvest weight you will be feeding this rate or slightly less 1.5%) (good place to put your safety net)
4. Nitrification rate 0.45 (this is unknown for clay media in a static environment - if someone knows this, let me know - for this I will use the "norm" for a fluidized moving bed which will be higher than a static grow bed but we make up for that in the bio filter efficiency below)
5. Bio filter efficiency 20% (this is quite low, commonly 50% or higher but your bio filters are full of solids so the efficiency is greatly reduced)
6. Passive nitrification 10% (this is the nitrification happening outside of your grow bed, pipes and fish tank)
7. Culture density 10kg/m3 (a good place to start)
8. Number of fish 20 (500grams)

The results from above suggests n 203grams per day of feed with 100liters of expanded clay. In this scenario roughly 2grams of feed per day per 1 liter of expanded clay.

If you change any of the above assumptions the required filtration will change with it. A few examples:
Double the stocking density, your media amount doubles.
Increase the protein in the feed and the media amount increases.
Increase your feed rate, the media must increase with it.
Increase the bio filters efficiency, the amount of media needed is reduced.

And so on it goes....

Now that you have figured out your TAN removal, you can work out your flow rate. Unfortunately this is also complicated and I am not able to simplify it for you. However, it is calculated from the following:
(TAN available after effluent removal) / (desired TAN concentration (generally 1.8mg/L) x (the biofilters efficiency to remove TAN).

The resulting number for the TAN removal above is 16L/min. 16 x 60 = 960liters/hour. Considering the fish tank volume is 1000liters + grow bed volume 100litres (if we have 100liters of clay) the total volume of the system is < 1100liters with a flow rate of 960liters per hour. I will suggest that my minimum guideline of turning over the system water once per hour is sufficiently adequate for those starting out. If anyone has less than 100liters of expanded clay and more than 10kg/m3 you will have time to expand on your growbeds. Though I would guess most members here will have more than two bags of media.

I respectively suggest you keep this in mind, Gary when next you are generalizing with your "mythconceptions".

Cheers
Paul V

[GaryD]

Hi Paul,

Perhaps Gary, you would like me to offer the formula for calculating if your bio filter (grow bed) is adequate, before you get the fish? I thought this would have been in your book mate...

Because the formulas are complicated I will give you a few examples. This calculation has a very large safety net and many assumptions.

The reason the complicated formula that you have provided is not in my book is, quite simply, that no-one would apply it.

The only safe way for a small aquaponicist to know that they are managing water quality within appropriate parameters it to undertake water tests and to manage their systems according to the results.

Your knowledge and skill around aquaculture is evident (and largely appreciated) but you are less well informed when it comes to understanding the behaviour of backyard food producers.

Very few backyarders are going to commit the resources (time, money, etc) to develop your knowledge and skills......or even those required to become successful commercial operators. Furthermore, they are not going to spend the money to buy the sort of equipment that you routinely handle in the course of your commercial consultancy work.

While this may limit them in some respects, most of them will be able to grow clean fresh food to some extent. My job is to help them do it better.....but I understand that that's an incremental process.

I've been battling simplistic guidelines (around basic things like the need for mechanical filtration) for over three years, and I'm only just starting to get traction now.

Gary

[Crusty]

Hi Paul,


The reason the complicated formula that you have provided is not in my book is, quite simply, that no-one would apply it.

The only safe way for a small aquaponicist to know that they are managing water quality within appropriate parameters it to undertake water tests and to manage their systems according to the results.

Your knowledge and skill around aquaculture is evident (and largely appreciated) but you are less well informed when it comes to understanding the behaviour of backyard food producers.

Very few backyarders are going to commit the resources (time, money, etc) to develop your knowledge and skills......or even those required to become successful commercial operators. Furthermore, they are not going to spend the money to buy the sort of equipment that you routinely handle in the course of your commercial consultancy work.

While this may limit them in some respects, most of them will be able to grow clean fresh food to some extent. My job is to help them do it better.....but I understand that that's an incremental process.

I've been battling simplistic guidelines (around basic things like the need for mechanical filtration) for over three years, and I'm only just starting to get traction now.

Gary

Well I am lost for words. I offered a sound starting point for people to include as part of their backyard designs based on years of commercial experience and I am not qualified to offer that advice because I do not understand the psyche of the backyardie.. Previously, it was because I have much to learn about aquaponics. The mind boggles. How my knowledge can not be transferred or scaled for the backyardy is a mystery to me.

I would think it an underestimation of peoples ability to understand a simply and safe guideline such as that. You will read in my previous post that daily testing of the water will be required for the first 4 to 6 weeks and if the system is not stable by then, your filtration is inadequate. Suggesting that testing the water and adjusting your entire system as you go is the only way for a backyardy to work this out is just plain odd. Especially, if the backyardy has no place to start from such as a guidelines for tank size, amount of grow bed and the minimum size for the pump. Without knowing these, how does one build anything?

It has become quite clear that I am wasting my time here as at every turn Gary you profess to know better. I find your disregard for solid science, proven in the field, to be offensive.

Good luck to you
Paul V

For those that are interested here is the formula:

That formula is 2grams of feed per day per liter of expanded clay. Everything else can be worked out simply from that and with a great deal of safety. If you are concerned simply multiply the resulting amount of media by 1.5 to add further safety margin.

How does this work? Very simple.
If you would like to grow 40kg of silver perch using your grow beds as filters. This is not about density I don't care how many tanks you have.
Multiply the 40kg by the feed rate of 2% = 800grams of feed per day for growth.
Divide 800grams by the 2grams (feed/day/liter of media) = 400liters of expanded clay.
To add more safety multiply that by 1.5 and you will have more than enough media to deal with the load.
Turn the total system water over once per hour.

The same formula can be worked from the UVI numbers of 180grams of feed per day per m2 of raft (based on 36% protein feed which is most fish feeds).

[GaryD]

Hi Paul,

Are you seriously suggesting that the following is something that most backyard aquaponicists are going to understand (much less apply)?

Because the formulas are complicated I will give you a few examples. This calculation has a very large safety net and many assumptions.

Assumptions made:
Surface area of expanded clay of 90m2/m3 (can be 2500 but when those pores are blocked with organics that number is drastically reduced to 90m2/m3 - always use worst case for biofilters as the activated surface area will differ from the actual surface area often lower.)
Feed protein 35% (majority of native fish feeds are around this mark though carnivore (barra) feeds are considerably higher - Also younger fish tend to have higher protein diets)
Feed rate 2% (this varies with the fish age but generally at the end harvest weight you will be feeding this rate or slightly less 1.5%) (good place to put your safety net)
Nitrification rate 0.45 (this is unknown for clay media in a static environment - if someone knows this, let me know - for this I will use the "norm" for a fluidized moving bed which will be higher than a static grow bed but we make up for that in the bio filter efficiency below)
Bio filter efficiency 20% (this is quite low, commonly 50% or higher but your bio filters are full of solids so the efficiency is greatly reduced)
Passive nitrification 10% (this is the nitrification happening outside of your grow bed, pipes and fish tank)
Culture density 10kg/m3 (a good place to start)
Number of fish 20 (500grams)

The results from above suggests n 203grams per day of feed with 100liters of expanded clay. In this scenario roughly 2grams of feed per day per 1 liter of expanded clay.

If you change any of the above assumptions the required filtration will change with it. A few examples:
Double the stocking density, your media amount doubles.
Increase the protein in the feed and the media amount increases.
Increase your feed rate, the media must increase with it.
Increase the bio filters efficiency, the amount of media needed is reduced.

And so on it goes....

Now that you have figured out your TAN removal, you can work out your flow rate. Unfortunately this is also complicated and I am not able to simplify it for you. However, it is calculated from the following:
(TAN available after effluent removal) / (desired TAN concentration (generally 1.8mg/L) x (the biofilters efficiency to remove TAN).

The resulting number for the TAN removal above is 16L/min. 16 x 60 = 960liters/hour. Considering the fish tank volume is 1000liters + grow bed volume 100litres (if we have 100liters of clay) the total volume of the system is < 1100liters with a flow rate of 960liters per hour. I will suggest that my minimum guideline of turning over the system water once per hour is sufficiently adequate for those starting out. If anyone has less than 100liters of expanded clay and more than 10kg/m3 you will have time to expand on your growbeds. Though I would guess most members here will have more than two bags of media.

If so, you're blowing smoke.......and you're one of the reasons why people are likely to rely on simplistic "guidelines" rather than taking a more considered approach.

Your formula contains at least one typo......and contains terms like TAN which most backyarders wouldn't understand.

If you spend more time making a genuine effort to simplify and educate and less time lecturing and posturing, you'll be able to connect more readily with your backyard audience.

Now Paul, given your own taste for very direct language, I know you won't mind me pointing that out.

If you're expecting people to understand something like this.......

That formula is 2grams of feed per day per liter of expanded clay. Everything else can be worked out simply from that and with a great deal of safety. If you are concerned simply multiply the resulting amount of media by 1.5 to add further safety margin.

How does this work? Very simple.
If you would like to grow 40kg of silver perch using your grow beds as filters. This is not about density I don't care how many tanks you have.
Multiply the 40kg by the feed rate of 2% = 800grams of feed per day for growth.
Divide 800grams by the 2grams (feed/day/liter of media) = 400liters of expanded clay.
To add more safety multiply that by 1.5 and you will have more than enough media to deal with the load.
Turn the total system water over once per hour.

......you're probably going to enjoy greater success.

If I understand you correctly, you're saying that I could keep 40kg of silver perch (feeding them 800g of feed per day) in a system with 600 litres (allowing for the 1.5 safety margin) of clay pebbles for bio-filtration.......and putting the water through that bio-filter (grow bed) once per hour.

Is my understanding correct?

What other assumptions are in play?
Are we removing solids?
Does the formula vary from continuous flow to flood and drain?
When you say "This is not about density. I don't care how many tanks you have.".....can you explain what you mean?

Gary

[Crusty]

Ahh I see your point Gary, duly noted. I apologize to those readers that interpret my posts as being lecturing and posturing. I will keep your feedback in mind for future communications. Please disregard my previous posts relating to filter sizing and flow rates, as Gary pointed out, it may be interpreted as misleading and ambiguous. I am certain that Gary will be able to provide you with a more suitable approach as he has greater experience in back yard aquaponics than myself.

Thanks and good luck.
Paul V

[DaveOponic]

All very amusing but a little tedious. I agree with Gary on this. The average backyard AP'er wants to produce healthy organic fish and vegetables without too many complications.

Leave the theory, statistics, formulas and calculations to the commercial "experts."

I do have a complete test kit for pH, ammonia and all the other variables. I have it in the shed where it's been for over two years. I have used it to measure my swimming pool Chlorine, hardness and pH, as well as my AP water.

These days, I rarely need to test. The water's good, plants are healthy and so are the fish. They tell me if they want more food by splashing at the surface for more pellets. If the plants start to yellow their leaves, I add some seaweed ferttiliser.

At the risk of stating the obvious, once you have got the system running, made a few mistakes and learned from experience and others, everything can bubble along nicely. You can put away your "beginner's Guide to Aquaponics" and your test kit and calculator and enjoy smoking fish, having BBQ's and harvesting fresh organic vegetables. That's why I do Aquaponics.

[GaryD]

Hi Dave,

I agree with Gary on this. The average backyard AP'er wants to produce healthy organic fish and vegetables without too many complications.

Leave the theory, statistics, formulas and calculations to the commercial "experts."

Let's be careful to separate out the issues here.

To avoid confusion, let me say that some of my remarks have more to do with Crusty and I (both of whom have healthy egos) being able to work together effectively than any view on my part that we ought not do the aquaponics job properly.

While I agree that we need to simplify things (where practicable), I also believe that, if people are in any doubt about whether they have things right, they need to undertake (and respond to) water tests.

I think we also need to differentiate between simplify and simplistic. Simplify is good, simplistic is not.

Crusty and I will agree about much more than we will disagree about.......particularly when it comes to the creation and maintenance of a suitable environment for the production of fish as the cornerstone of successful aquaponics.

Gary

[Crusty]

At the risk of stating the obvious, once you have got the system running, made a few mistakes and learned from experience and others, everything can bubble along nicely. You can put away your "beginner's Guide to Aquaponics" and your test kit and calculator and enjoy smoking fish, having BBQ's and harvesting fresh organic vegetables. That's why I do Aquaponics.

Personally, I would not be advising a beginner to take this approach, as we were discussing. However, it sounds like you have it worked out mate. I believe you have described the point of aquaponics well.

[ash33]

Well I found the thread very informative