Backyard Aquaponics
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Hello do you have any idea about the required surface of filtermedium per kg food per day ?
I saw the calculation metric model, but the values doesn't makes sense to me.

We're using 400L plastic media like kaldness (700m²/m³), have 16 squaremeters growbeds which cycle 15min every hour and feeding 1,5kg food per day.
Nitrite is all the time 0,8mg/l.
We're running the hole system once per hour throw the filter but NOT complety through the growbeds.
But 0,4m³*700m² => 280m² surface thats like 1m³ gravel and 1,5kg food should also be fine isn't it ?


Thanks
Dom

What about temperature? Ph? How accurate do you need to be?
Is the system cycled yet?
What fish do you have?
What results did you get with your smaller system before you expanded to 17
6 sq metres of growbeds?

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System is running for three years.
Ph is 6.8 and temp actually 20.3°C
We're using common carp, but missed the formula for the biofilter size of surface and pumping liter per hour.
Actually we pump hole system every hour through the filter.
And growbeds only 15 mins per hour.

Excelsheet means only 5m3/h but a lot more growbeds but my idea was to work with a biofilter instead of only growbeds

So i read a lot of uvi and tan etc.
But help me:
1000g food with 36% protein is for 10m2 fruting high nutrient requirement.
10m2 * 0.3m deep of gb = 3.33m3 gravel
3.33m3 × 300m2 surface = 1000m2 surface needed
We have 16m2 but not pumping the hole system (35m) through the gb, but through the filter with 400l helix (700m2/m3)
So how much water should run through the beds ?
700*0.4 = 280m2 biofilter missing 720m2 ?
Is this correct ?

Gesendet von meinem SM-G900F mit Tapatalk

Tiggar PMed me to help. Anyone else wants to do that I can't promise I'll pop in to help but I get an email when I get a PM so I get prompted to visit the forum.


This question is a bit tricky so I'm going to ignore it for now.



First thing is to calculate the TAN production.

P TAN=F x [Protein] / 100 * 0.092

Where:

P TAN = production of total ammonia/ammonium nitrogen in kg/day
F=Feed fed per day in kg
[Protein]=Percentage of protein in feed (0-100)

So:

TAN= 1.5 x 36 / 100 x 0.092
TAN= 0.0497kg/day

Second thing is to calculate the volume TAN removal rate

VTR = ATR x Specific area

VTR=Volume TAN removal rate in mg/m3/day
ATR=Area TAN removal rate in mg/m2/day = approximately 300mg TAN/m2/day
Specific area= of gravel equals ~300m2/m3

therefore:

VTR= 300 x 300
= 90,000 mg TAN/m3/day
= 90 g Tan/m3/day

Third thing is to calculate the volume of media required

V=(1-Is)P/VTR

where:

V=media, m3
Is=correction factor for nitrification that occurs on tanks walls, pipes and other wet surfaces (0=conservative 1=ridiculously optimistic) normal value is 0.3
P=P TAN=production of tan per day = 0.0497kg TAN/day= 49.7g TAN/day
VTR=90g/m3

Therefore:

V=(1-0)*49.7/90
~=0.6m3

If you use a "normal" correction factor

V=(1-.3)*49.7/90
~=0.4m3

Now unless I have stuffed up the maths any where this once again shows that the primary function of gravel beds is NOT biofiltration. In terms of biofiltration basically all GBs are massively over sized.

Hey Stuart,
thanks a lot for your fast reply.

We're using helix with 700m²/m³ so i correct the formula:
VTR= 700 x 300
= 210,000 mg TAN/m3/day
= 210 g Tan/m3/day

V=(1-0)*49.7/210
~=0.25m3

So we have the correct amount (400L) of biofilter.
But we pump every hour the both growbeds with each 2000L gravel.
I think the growbeds make same extra surface, or can't calc i with them cause the short time of pumping and small amount of water ?

Yeah but with the helix you are already getting enough biofiltration. Any thing you put through the GBs is extra.

Problem is that the nitrite is 0.8 and still constant.
When i decided to feed 1.8kg the nitrite raise.
Since 3 weeks we had the same readings.

I was told that temperature affects your VTR as well. The colder it gets the slower the bacteria will work.

The formula I was given was VTR = (temperature in deg celcius x 0.0556) - 0.092

If it drops below 8 degrees C you will have less than 300mg/m2/day.


Also for flowrate you can try this calculation

Flow rate to remove TAN = TAN production (Kg/day) / (50 x (desired TAN (mg/L) / 1000000))

But if you have an ammonia test kit you can try measuring the ammonia each day to see if bio filter is working?

Yes there is no ammonia left.
Only nitrite is still 0.8mg/l and we don't stop feeding...

It can take quite a while for the nitrite to drop. Three weeks does seem a while though.

Also my flow calculation was in L/day, to convert to L/ min just devide by 1440

Do I remember rightly that your flow is 5m3/hr?

Maybe try to get your pH above 7 or slow your flow rate to keep the water on the media longer?

If anything you would want to increase the flow not decrease.

The other thing to check that I just thought of is to check that the bacteria are getting enough oxygen. Never a problem with trout because if you get to a situation were the bacteria don't have enough oxygen then they are dead. Carp are hardier though.

Any photos of your system?