TheDictator

System idea based on Pauls Dual loop

97 posts in this topic

Swede - there are a couple steps to figuring that out.

First - what nitrate level do you find acceptable in the RAS component? 200? 500? 800? 1000?

Second - What is the maximum you will be feeding the fish a day? I.E. Right before you harvest and you have maximum fish poundage.

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400 gallons fish tank volume,

80 tilapia grown out to 500grams.

40 kg total weight at grow out size. Maximum feed 1% of fish weight, 400 grams of feed.

I might go higher on fish stocking but felt this would be very safe to start with.

As far as acceptable nitrate level.. I don't know right off what would be ok for tilapia. I guess if possible around 200ppm or below.

I need to read the book about RAS by Timmons and figure

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Can i assume 32% protein feed?

 

daily TAN production = 400g Feed * .32 * 0.092

daily TAN production = 11.78g 

Daily Nitrate-N production = 11.78g nitrate-N

Daily Nitrate production = 11.78g x 4.4268 = 52g

 

Once the tank reaches steady state, inputs = outputs. 

so a 1% water change daily would mean 5200g/1500l = 3400mg/L Nitrate.  Yikes!

5% daily = 1040g/1500l = 690 mg/L steady state

10% daily = 520g/1500L = 345 mg/L steady state

 

I'm "comfortable" with 690mg/L Nitrate for Tilapia. That means you'll need to transfer at least 20 gallons a day from the RAS loop. Which means you need to evaporate / transpirate /dump at least 20 gallons from your grow loop every day.

 

If Paul is watching this - am I on the right track?

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Very excellent break down Mr. Mathews!! Couldn't have said it any better myself.

 

 

Which means you need to evaporate / transpirate /dump at least 20 gallons from your grow loop every day.

 

And this will be the trick in the matter...

 

Might be possible to look at what Dr. Lennard suggests in his grow bed to fish ratio, which might kind of help in a small way at a starting point.

 

And I would think involving a good mix of plants since some plants are very heavy nitrogen feeders, low water consumers while others are slow nitrogen feeders, higher water consumers.

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I am not following your math Matthew,

I am with you up to 11.78 grams of nitrates. 

Where does the 4.4268 number come from? also we assume 1500L (this number is strictly for the fish tanks not including any filtration tank or sum volume) That was my fault for not specifying. We can still use 1500L for simplicity..

If that is correct then we have 52000mg of total nitrates being produced per day in system. 

52000/1500L= 34.6mg/L or 34.6ppm Nitrate a day per liter. 

So if we take out 15L we take out 34.6*15=520ppm Total nitrates per day.

 

Simply put, relying on water changes isn't going to control the nitrates at a high stocking density. Only denitrification will.

At the rate above 34.6ppm/day it will take 14.5 days to reach a 500ppm Nitrates without any water changes and without any denitrification.

 

I believe there will be some denitrification in the system still.. But I have no idea of knowing at what rate that may or may not happen at.

 

Still Paul said denitrification isn't necessary in the Fish loop if designed properly.. ???? 

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4.4268 is the conversion factor from Nitrate-N to Nitrate. 

 

 

Denitrification is not the answer.

 

Your math is missing the nitrate that is already in the water. As I showed earlier, a 1% water change will leave you with a level of 3400mg/L, but it won't go higher than that. at 3400mg/L, taking 15L = 51g of Nitrate. See how it works?

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Swede, it is 1000 mg to 1 gram. The 4.42 is the coversions of nitrate nitrogen to nitrate ions, which nitrate ions is what matters; remember that post I made on the byap mineralization thread. :)

To be honest, I didn't check his math. Will do once I get home. Looks about right.

Nitrates are still being controlled to a small extent but this will ultimately all depend on your plant volume and configuration

Due to the pollutant equilibrium, really would take around about a 60% water change rate to make an impact, but this is not necessary either. However, if your plant loop is built properly, then there would be around a 90~100% water change rate, but this would require skills that is above our pay grade. ;)

Otherwise, since we are just hobbyists, I think could make up the difference with closed loop wicking beds

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Mr. Mathews da man. BTW, sorry about potentially screwing you on the seeds from Chatterson. I actually feel bad about how how all that went down.

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BTW Timmons states that he has run salmonid recirculating systems at levels of 1,500mg/L without impact on the fish. I can only assume that if Salmon/Trout can handle it, Tilapia will do just fine.  And setting the max at 1,500mg/L can be done with a 2.25% water change. So 34 Liters a day minimum.

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Crsublette,


I know 1000mg is 1g. Sweden is a "metric country". ;)


I did forget that 1g ammonia makes 4.42mg Nitrate. Thanks.


 


Matthew,


Once the tank reaches steady state, inputs = outputs. 


so a 1% water change daily would mean 5200g/1500l = 3400mg/L Nitrate.  Yikes!


5% daily = 1040g/1500l = 690 mg/L steady state


10% daily = 520g/1500L = 345 mg/L steady state


 


where I got confused was here:


1% water change daily would mean 5200g/1500l = 3400mg/L Nitrate.


 


Where is the 5200grams coming from?


- The daily input is 52grams or 52000mg total in a 1500L system.


- 1% of 52000mg is 5200mg.


- 5200/1500=3.47mg/L


 


What do you mean by me not accounting for nitrates in the water? This all depends on how long the system has been running up until this point right?


Or are we assuming something  that I have missed?


 


I am really tired and have been doing books all day so numbers are spinning in my head. Hope you don't mind clarifying?


 


Thanks!

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400 gallons fish tank volume,

80 tilapia grown out to 500grams.

40 kg total weight at grow out size. Maximum feed 1% of fish weight, 400 grams of feed.

I might go higher on fish stocking but felt this would be very safe to start with.

As far as acceptable nitrate level.. I don't know right off what would be ok for tilapia. I guess if possible around 200ppm or below.

I need to read the book about RAS by Timmons and figure

 

At maximum biomass you will be exchanging around 54 liters per day to maintain nitrate at 200mg/L

Edited by Paul Van der Werf (see edit history)
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Crsublette,

I know 1000mg is 1g. Sweden is a "metric country". ;)

Nevermind. I did not pay attention to Mr. Mathews units. He did a " g " that should've been a " ml ".

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the 52grams (the daily Nitrate production) is 1% of 5,200 grams (the total Nitrate in the tank). Kinda impressive - 5.2Kilos of Nitrate!

 

this works because in the steady state, input=output.  It's a little bit of an engineering shortcut to design for the maximum load.  So you're right in wondering where the total nitrate in the tank came from - but if you worked it out on a spreadsheet, showing every day you removed 1%, and every day you added 52g Nitrate, eventually it would touch 5200g Total Nitrate. 

 

 

where I got confused was here:

1% water change daily would mean 5200g/1500l = 3400mg/L Nitrate.

 

Where is the 5200grams coming from?

- The daily input is 52grams or 52000mg total in a 1500L system.

- 1% of 52000mg is 5200mg.

- 5200/1500=3.47mg/L

 

What do you mean by me not accounting for nitrates in the water? This all depends on how long the system has been running up until this point right?

Or are we assuming something  that I have missed?

 

I am really tired and have been doing books all day so numbers are spinning in my head. Hope you don't mind clarifying?

 

Thanks!

 

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Can i assume 32% protein feed?

 

daily TAN production = 400g Feed * .32 * 0.092

daily TAN production = 11.78g 

Daily Nitrate-N production = 11.78g nitrate-N

Daily Nitrate production = 11.78g x 4.4268 = 52g

 

Once the tank reaches steady state, inputs = outputs. 

so a 1% water change daily would mean 5200g/1500l = 3400mg/L Nitrate.  Yikes!

5% daily = 1040g/1500l = 690 mg/L steady state

10% daily = 520g/1500L = 345 mg/L steady state

 

I'm "comfortable" with 690mg/L Nitrate for Tilapia. That means you'll need to transfer at least 20 gallons a day from the RAS loop. Which means you need to evaporate / transpirate /dump at least 20 gallons from your grow loop every day.

 

If Paul is watching this - am I on the right track?

 

52 grams (52,000mg) of NO3 in 1500 liters is 35mg/L per day.  Check your calculations.

Edited by Paul Van der Werf (see edit history)
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Welp, just got back home... will throw some documents up here that might help and will run this through my spreadsheet.

 

Not for sure what calculations Mr. Van der Werf is doing and would love to be informed of this or an article or explanation that gives us it...

 

So, just a sec...

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@200mg/l we have 300000mg total nitrates in 1500l of water.

I still am missing something.. 54L x 200mg/L=10800mg removed.

If removed at a concentration of 352000mg or 235ppm then it's a total of 12690mg removed. How can that compensate for 52000mg added daily?

What an I missing? This is driving me nuts!

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From what I understand, essentially the "dual loop" system is explained by dilutions and equillibriums.

 

The best I could was a quick explanation of what I understand of Pollutant Equillibrium in post#34 in thread Aquaponics, Aquaculture Filtration - Purchased Equipment Vs DIY

 

Here is an article that talks further, but I do not know how applicable their calculations are in our context. The article mainly talks about UV devices effectiveness on pathogens, but I found it to be a good explanation of the practical application of this. Just think "aquaponics" instead of than "UV and pathogens" when reading the article.... Specifically, I think we are talking about "Scheme A" within this article. Pathogen Reduction in Closed Aquaculture Systems by UV Radiation: Fact or Artifact?

 

 

And another moment really quick to create this and run it through a spreadsheet

 

 

I initially learned this concept, that is dilutions and pollutant equillibriums, from Dr. Kevin Novak when he was introducing his Anoxic Pond Filtration for koi and goldfish ponds and watergardeners. ((if curious on this device by Dr. Novak, then check out his AFS blog and the Manky Sanke's AFS article and even an AFS eBook)).

 

Here is the explanation from Dr. Novak's perspective from an old PDF that is no longer available... I think it should be in the AFS eBook but I couldn't get it opened. This PDF is attached below... Below quote is from the PDF's page 10 through 11.

 

However, how much water should be renewed and how often should such changes take place are often a matter of discrepancy. Finding unambiguous answers to these questions in hobbyists’ books and monthly periodicals may become a crapshoot at best. Too many hobbyists do not understand the mathematical equations used to determine whether water changes would become beneficial or redundant in an enclosed ecosystem such as our ponds.

One thing hobbyists must understand is the idiom Pollutant Equilibrium (or PE for short). Pollutant Equilibrium means that the amount of pollutants that are being produced by the animals, plants, the filter, and the amount the water that is exchanged from periodic water changes, will reach what is called a steady state or constant state. This means when a steady income of pollutants are being produced at a given rate and water is being exchanged at a given rate, that everything will remain on an equilibrium with each other and nothing will increase or decrease over a given time. If pollutants overshadow the amount of water being exchanged, then the amount of pollutants will increase over
time to toxic levels, even though a constant amount of water is being replaced.

For example, lets say you have a pond, for the sake of argument will say this pond is 3000 gallons, that is producing 8-ppm (ppm = parts per million) of nitrogen (NO3) every month, this now becomes a constant. The hobbyist now wishes to reduce this nitrogen compound by doing a water change on a monthly basis. If the hobbyists were to do a 50 percent water change, this now would halve the amount of pollutants to 4-ppm (0+8)-50%= 4). However, do not forget that every month the NO3 levels will begin again to elevate another 8-ppm. In addition, you must include the NO3 compounds that were remaining from the last water change. The next month will make the pollutant level elevate to 12-ppm before a water change (4+8)-50%=6). The next month after that it will elevate to 14-ppm (6+8)-50%=7) and so on in their pond. It would now take eight months before a PE is then reached. Then every month afterwards, the Nitrogen compounds being produced, and the amount of water being exchange would be in equilibrium with each other, and would remain at a constant 15.9-ppm NO3 levels or a steady state. As you can see the hobbyists even after conducting a 50 percent water change of 1500-gallons, may still run into problems with cyanobacteria and algae buildup, as green water in the pond. Because their nitrogen compounds have now exceeded the safety margin of keeping nitrates below, the 15-ppm limit every month before a water change is executed. If the same hobbyists were only to do a 20 percent water change every month, it would take over sixteen months before a PE would be reached of 39.0-ppm NO3 levels. If the water changes were only 10 percent, calculation similar to those used above, would show the ensuring situation deteriorating even further, with the pollutants stabilizing at 20 times the amount generated from one water change to the next.

Besides, the PE values differing with different extent of water being change, the time it takes for PE to be reached also differs. In reality, doing a water change of anything less than 40 percent would be useless in anybodies pond. The consequences of increasing or decreasing the frequency of water changes or the volume of water replaced on each occasion would only be anyone’s guess. Do to the fact the hobbyists not knowing the exact aleatory nature of the biomass and how much pollutant matter is being generated in a single day of the pond existence.

Therefore, with the information that we now know regarding the build up of pollutants, and routine partial water changes, we can conclude the following. Starting with pure unpolluted water, pollutants in the pond will progressively increase with time, even as partial water changes continue at regular intervals. However, this increased does not continue unabated, but stabilize as it reaches PE. The greater the proportion and/or shorter the régime-time between each renew water change, the lower the PE would be, and the shorter the time it will take the PE goal to be reached.

As you can see, winning the battle against pollutants in an enclosed biotope such as our ponds seems almost to be futile1. This is because the amount of nitrogenous wastes produced is many times greater than the pond’s natural capacity to absorb it. However, one of the biggest weapons we have in our arsenal, which is in our favor, is a well-designed filtration system, which we can implement in the battle against the pollutants. Now we come down to the one big problem that all hobbyists are faced with, and that is “the well-designed filtration system.†Since this is easier said than done, the hobbyists are left with no other alternative than to do partial water changes in their pond.

 

 

Q&A - chapter 3.pdf

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I have explained this process many times......

 

I apologize for the inconvenience Mr. Van der Werf. I will see if I can find it...

 

" Repetition is the mother of pedagogy "  :)

Edited by crsublette (see edit history)

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52 grams (52,000mg) of NO3 in 1500 liters is 35mg/L per day.  Check your calculations.

Yes, 35mg/L per day in a 1 % removal situation will end up stabilizing near 3500mg/L. Takes about a year to get there though.

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@200mg/l we have 300000mg total nitrates in 1500l of water.

I still am missing something.. 54L x 200mg/L=10800mg removed.

If removed at a concentration of 352000mg or 235ppm then it's a total of 12690mg removed. How can that compensate for 52000mg added daily?

What an I missing? This is driving me nuts!

 

Not for sure either... I also am having a tough time following...

 

So... From what I understand and Dr. Novak attempted to teach through the PDF I shared above, here is the spread sheet using Dr. Novak's explanation as the formula...

 

The syntax is a follows from what I understand from his explanation and proves out to match Dr. Novak's numbers in his explanation example.

 

 

NitrateConcentration = regenRate + { previousNitrateConcentration - ( previousNitrateConcentration * WaterChangePercentinDecimal )  }

 

 

Late Edit :

 

Now of course just don't directly plug the Niitrate number derived from the Food Feed amount into the spreadsheet... You will have to dilute this Fish Food Nitrate mg/l according to your pond's (or tanks) volume. Wikipedia explaining the Dilution math part of this.

 

Grr... I should have added this dilution part.

PE.xlsx

Edited by crsublette (see edit history)

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