Backyard Aquaponics
A place to discuss aquaponics

VB wrote this on another thread and I have moved it to here so as not to go off topic on ROZ':



I am finding similar problems in that nitrate levels are rising but I have ample media and a small amount of fish, my cause however may have been the addition of "charlie carp" to the system - this may not increase the nitrate levels but may have decreased the amount the plants take up.

I have been looking at collecting data and seeing how the weight of fish to tank water stands up, with vb showing concerns, will post these figures weekly but first let the system settle down this week.

Start info required:
fish tank size
grow bed size
Number of fish (silver perch)
weight of fish (average)
weight of feed
type of feed (pellets, duckweed, greens)
PH reading
nitrate reading
silver perch FCR (use 1.6)

What is the amount of feed to body weight of SP?
I have seen an example using 2% for barra but can't find any other reference. Barra are voracious feeders and growers so will reduce that to 1% if no one has any other info.

Les - I think I need to clarify what I meant. I was not talking about nitrate levels. I was talking about the ability of the nitrosomonos and nitrobacter to convert the wastes - ammonia to nitrite and nitrite to nitrate. The more i think about it though - the more I think I have unrealistic expectations. It is to be expected I guess that int he 12 hours following feeding I will register some ammonia and nitrite in the water. The levels that I am finding are not dangerous.

What you are doing is still relevant though.

BTW my nitrate levels are very high - because I still don't have that many really vigorous plants. At the levels I am running (between 80 and 160 (closer to 160 I expect) the fish are having not problems. They are happy and in good health.

Starting figures:
Tank size - I have 2 tanks which are filled to 300 litres each but seeing it is the density of fish stated (maximum 6kg/100l) then I will work on 300litres

Grow bed size - 2 GBs filled to 460litres of 10mm gravel (GB to fish tank ratio 2:1)

Using these figures the fish tank will support 18kg of fish weight and the GBs will support 27.6kg - maximum supported weight = 18kg

Number of silver perch = 33

Weight of fish 70 grams ave (caught 2 and approximated using one as the average size in the tank)

PH reading 7.2

Nitrate 100

total fish weight 2.31kg - well under the 18kg max level

Daily fish feed 23 grams (I have been feeding ~30 grams)

Using FCR of 1.6, SP total weight should have increased by 1kg in ~ 2 months - or ave weight then 100grams each

In one of my 30 gallon guppie tanks I'm running with nitrates of 180 plus, this system is in the basement using a shallow 4in deep grow bed and only a few tiny toms a house plant and one onion.
I'd love for us to get data together on the ratios of fish, tank size, nitrate levels, and plants growing as this would give us all a good idea of the systems capabilities? One of the major varabiles being feed amount, or would that show up as nitrate readings?
Whats the thought?

pretty much the only two variables for nitrate are feed and plants. feed in = nitrates and plant growth = nitrates out.

if the two are balanced then the nitrates will sit solid where they were when balance point was achieved, be it 10ppm or 110ppm.

No probs vb, I was going to do this anyway (wasn't thinking of publishing the results tho) - with nitrate levels, mine are reasonable atm but wondered if adding things like seasol etc could possibly upset the nitrate uptake by the plants (short term).

Just to clarify, my plants were looking a bit daggy (in the eyes of the wife) so added some charlie carp as a pacifier, plants looked better afterwards (her observation) but the nitrate levels increased so stopped feeding the fish - this is what got me thinking along these lines.

Using the figures you put up - 500litres of GB and 150grams of food:
your GB will support 250l of fish water (2:1 ratio) and 15kg of fish

Now using 150g/day @ 1%, makes fish weight @ 15kg (~500 grams/fish), which is the capacity of you GB.

So this can either prove/disprove/modify the figures we are using:
maximum 6kg/100l of fish water
GB ratio 2:1
FCR
food to fish %
food to fish conversion

I think most of them will be spot on but why not find out, any comments welcome

The amount of water in my system, comprising what is in the fish tank and what is in the sump, is approx 1500 litres. At 6kg per 100 litres, this would support 90kg of fish. My grow-bed holds approximately 500 litres, so on the 2:1 grow-bed to fish tank ratio this grow-bed limits the stocking density to 15kg.

Number of silver and jade perch = 30, but 5 of these were damaged in early life by the fish shop and are destined to always be small. Accordingly I will say 27.

Weight of fish - I have absolutely no idea, but I reckon an average of 250 grams might be in the ball park. Therefore total fish weight approx 6.75kg - well under the 15kg maximum level.

PH is now stable at 7.2 due to the addition of CaCO3.

Nitrate is very high at somewhere between 80 and 160 *closer to 160 than 80 I reckon). Reason for this is that although I have 500 litres of grow bed - it is not fully planted and has few really heavy nitrogen feeders in it. The plants are not growing as well as they should because of their full sun situation. I will rectify this with my next system. People should remember that the 2:1 indicative ratio relies on the beds being well planted.

Daily fish feed approx 150gms.

Using FCR of 1.6 (Jade perch may actually have a better ratio) - total perch weight should increase by 94gms per day.

On my weight estimation (6.75kg of fish currently) I am feeding my fish about 2.2% of their body weight per day and if I was to maintain this level I would need to increase feed rate by 2 grams a day.

Who knows what % of body weight you are meant to feed your fish per day to get optimum growth?

I think it varies at different stages of their life. I think for silvers, it's like 6 or 7 % as fingerlings down to 1% as they get plate sized. Can't find the link to that info..... will try again and report back if I find it

Start info required:
fish tank size - 10,000L

grow bed size - total 8000L varying sized gravel, sand and coco peat

using the - 6kg : 2 GB : 1 fishtank
we have - ?kg : 0.8 GB : 1 fishtank
can support - 240kg

Number of fish (silver & jade perch) - 247

weight of fish (average) - jades 40g (4.92kg), silvers 15g (1.86kg) = (6.78kg)

weight of feed per day - 2 feeds of about 100g each = 200g

type of feed (pellets, duckweed, greens) - barra pellets, duckweed, silverbeet, bugs, worms etc

PH reading

nitrate reading

silver perch FCR (use 1.6) - grown from about 5g each to 15g (from 0.62kg to 1.86kg in 7 weeks)

jade perch FCR (used 1.2) - grown from about 15g each to about 40g (from 1.845kg to 4.92kg in 7 weeks)

You people amaze me, I thought I would be in the minority and thus hadn't thought much of publicising my intentions on this subject.

Might see if I can embarrass myself and attempt to write a small program to automate this, after reading a few of the cv's recently - that shouldn't be difficult to do

some one had an excel file on food to fish sizes, should be in the downloads

I wasn't going to use excel and doesn't that only do a few calculations?

Have a copy of Delphi6, best see if it will run on vista first

Les did you find this download http://backyardaquaponics.com/forum/dlo ... file_id=19
this is the one I was talking about

That spreadsheet - and the theories behind it - can be a handy guide, but it would be better if the slow down in the conversion rate/feeding rate (and therefore growth) as the fish get bigger was built in. If you graphed the true relationship - it would not be a stright line - but would rather be curved.

For tilapia, the optimal feed rate starts at 15-20% of body weight for fry, up to 1-1.5% for eating-sized.

Start info required:
fish tank size ~500 liters
grow bed size - ~600 liters (max fish load = 18KG)
Number of fish - (tilapia) 62
weight of fish (average) - 20 grams (total fish weight = 1.24 KG)
weight of feed - 35 grams (2.8% of body weight. That's lower than I'd like I'm increasing it cautiously to make sure the filters can keep up.)
type of feed - mostly floating pellets, some leafy trimmings.
PH reading - 7.2 steady
nitrate reading - 40-80
nitrite - 0
ammonia - 0