Backyard Aquaponics
A place to discuss aquaponics

Hey, so we have 4, 750L fishtanks now. They all connect by gravity to a 200L swirl, continue by gravity to a 200L bio filter filled with plastic netting, from there it flows into two 150- 200L growbeds, finally it drains into a 100-250L sump and is pumped back to the fishtank.

The water is still pretty green and murky, although spray painting the sides of all the totes with green paint has made the bulk of algae growing on the sides dissapear.

Fish however keep dying, and its usually the biggest ones in the tank, some 3-4 inches long. I definitely think they are still overcrowded as we had 2200 fingerlings and id say around 200 if not a few dozen more have died. Would a lack of DO be the cause for the bigger ones dying?

Theres 4 airstones coming from a 170gallon airfilter in each tank..

The water temp has been quite low lately as it hasnt been very sunny but we have 2 300 Watt heaters in each tank, keeping them all above 72F

Another thing im worried about is the filtration and flow rate.

My main concerns right now are, do we have enough DO,? at the size the fish are how many should be in each tank? Do we need more growbeds to help filter the nitrates/nitrites? And how important is the flow rate of the system/what should it be at?

We have the flow rate maxed out before water starts spilling over the side.

Thank you so much again for your time

..
Sounds like you have got a good system set up..
There are likely many questions needing to be answered before the correct answer is hit upon..

DO is an obvious first issue and especially if you have green water.. Nitrites etc. Is a serious one to quantify, along with how long it has all been running..

The start would be to stop feeding until settled.. Salt, and possibly with callcium chloride, to help the fish cope

So, firstly what are the ammonia readings etc..

The linear system you have, is likely efficient, but the drag of all that, will slow the flow, and as you say, you are limited by things not flooding or overflowing..
Given the Rule-of-Thumb of a Ft change each hour, I wonder if you are getting there..

As you suggest that you have the pump throttled back to prevent overflow, I wonder if a rejig is practical, to redirect flow from the swirl filter back to the FT.. just to get max flow thru the FT..
this can be via a slightly raised return pipe from filter to FT, AND a tap to to the rest of the system ..
..
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Just re-reading.. four by 750L fish tanks.. and over two thousand fish..

How are the four connected.. in series or parallel.

I would hope in parallel, and with about a 5000L water pump, if not more to allow for tap back pressures..

And.... thinking of your setup.... AIR is soooooo important to all including the bacteria..
I have air stones in EVERYTHING.. just so the water returning to the FT is already oxygenated...

So.. . First.. stop feeding, then get the FT flow up and then get rid of MANY, MANY fish. And then those. Extra Grow Beds or media beds
Naturally... you can do nothing and wait to see how many fish you get left with, but chances are, there will be a major collapse, with sooooo many fish
.

When stocking, stick to 1 fish per 25L of wet media.

You are horribly over stocked. Get rid of some fish, and get some more growbeds.

I thought the same thing. Going along with BuiDoi, what are your readings of ammonia, nitrites, nitrates, and pH?

As the others have said you are massively overstocked for your filtration you have,your system layout seems ok,providing as Bui Doi says your grow beds are in parallel.Working on your figures say you have 2000 fish of approximately 3 to 4 inches in length this gives a total weight of 500 ib of fish,a 3to4 inch fish weighs approx 4 ounces,so ammonia production per day is about 50 grammes.Ammonia removal rate is quoted at 0.05 grammes per ft2 of media per day,therefore required amount of media,working with crushed granite which has a BSA of 35 ft2 you need a minimum of 28.5 ft3 of gravel to remove this amount of ammonia.
If you stocking was 200 3 to 4inch fish these figures come out at 50 lb of fish producing 5 grammes of Ammonia per day requiring 3 ft3 of gravel to remove this amount,these figures change depending on the type of media being use,if your using pea gravel the bsa is much lower requiring a much larger amount,or something like k1/k3 in a moving bed filter much less.But if you had 2000 fish at grown out size,we will say a 12 inch fish,this weighs about 1lb,then these figures come out 114.5 ft3 of media at a bsa of 35.
Your using a method to remove solids,which is good as it reduces the oxygen requirements of the filter beds making them more efficient,your net filter is a bonus filter,we dont know the bsa of netting so its hard to quantify,but it is an important part of your filtration.
You should make an effort to clear up your green water,not for the Tilapia they will sieve these particles out of the water,but its detrimental to your filter efficiency as for the algae growth on the side walls,again the Tilapia will spend all day browsing on this.
Flow rate through your filters should be once per hour or even twice per hour with high stocking,with the required amount of filter media retention time should be ok,so as said if you cant achieve this you either rework it or reduce stocking even further.
Water parameters for health of Tilapia are DO of 3 to 5mgl,these are optimum levels for your bio filtration,although Tilapia will survive at lower levels your filters wont,Ammonia at levels of 2mgl will start seeing them die.Nitrite levels of 5mgl the same,but anything over background levels will have a detrimental effect long term on the fish.
If it was me with your set up i would have a stocking of 100 fish of that size,then as i learnt how to keep fish increase that figure slightly.

Dasboot. I'm interested in this one because I have similar growbed volume though nowhere near as much water in my system. But your maths and the metric and imperial complications are a bit much for my slowing brain.

The way I look at it, 2 x 150 - 200 L growbeds = 300 - 400 L growbed space = probably maximum of 300 L wet media = about 12 fish using the 25 L wet grow media per fish you plan to grow to plate size theory.

I know that the swirl and biofilter help out with ammonia and nitrite and to a lesser extent the nitrate. But do they help enough to have nearly 10 times that many fish... or is my maths way out?

if 100 (which is admittedly a lot less than 2000) is a safe stocking level with these parameters, I'm building external filters this weekend!

Ok,100 fish at 3 to 4 inches is about 25ib of fish,these will produce on average 2.5 grammes of ammonia per day,with the average removal rate at 0.05 grammes per ft2 square of media per day,using crushed granite at a BSA of 35,you will need a minimum of 1.4 ft3 of media to remove this,so if my maths are right this equates to 0.05 m3 or 50l.
Now with those fish at pan size this would give us the requirement of 5.7ft3 of 35 bsa media,this equates to 0.16 m3 or 160l of 35 ft2 per ft3 media.
When i posted my reply it was more of an indication to the op how over stocked he was,i was using Aquaculture figures which we know dont use grow beds for solids collection and mineralisation and have a surplus of DO,RAS uses a figure of Ammonia removal of 0.05 grammes per ft2 or .005 m2 of media,if you have a media of known surface area its easy to work out how much you need,but this is not taking into account solids collection within this media as used in AP which is what the quoted figure of 20/25l of wet media does,
For an example if you were to use a moving bed filter with K1 with adequate solids filtration before you wouldn't require anywhere near 25l per fish.

Thanks dasboot... appreciate the time taken to explain. And apologies to the OP for slightly hijacking, although I think all responses have given consistent message that many many fish need to find another home.

Dangerous Dave,no problem at all,its good to get asked,there are many newcomers to AP that have no ideal on keeping fish to me its the most important part,in fact i would say the most important part is how to keep WATER.

+1

Ironically, that sums it up... how to keep water quality correct, and I might remain presumptuous to suggest that we all look for magic pills that can assist with readings..
There is nothing new in this post.. so many of us are seeking any technique that will allow higher fish densities.. and with varying results..

The interesting thing is the lack of response to the questions about readings, as this alone would qualify the responses being given..

I can easily relate to the OP, as I have lost soooo many fish from my first system, with consisteently low TAN readings etc..
I don't have any ability to read DO, but with air boiling into every water body, I can't imagine O2 being and issue..
Four days.. that has been the survival time following the orriginal collapse.. 99% water changes and settling times saw no improvement, except that the last one has seen Silvers survive past four days.. clearly, in my mind, my issue is SOMETHING in the system, that is or was toxic to SOME fish... (the Koi are very happpy)

My point... that we are not working for CSI. with spectrum analysis available 24/7..

Back to the OP... It would be good to hear just how the FTs are organised.. I am still concerned about air quantities..and distribution..

I would like to commend the OP for the good attempt at his system.. reference to solids filtering is reassuring..

I have asked the question that remains unanswered.. ".. and what RuleOfThumb ratio of fish to MEDIA " do you suggest when ALL solids are removed..

Clearly, no one has a figure, but the data may be found within some of the commercial AquaCulture designs, IF .. IF... you are good at working out the maths..

My new system, with 100% solids removal, has only 300L of clay as part of the bio-filtration, and with 100 Silver Perch in a 900L tank, I nervously watch those TAN readings, but they are encouraging..

Naturally, I anticipate having to do water change to reduce. NITRATES... but still wonder if there is a magic PILL, that can be used to help control both Nitrite spikes and Nitrate levels, and thus reduce the need for water change.
Peter

PS... I am interested in the different vessels we use as fish tanks .. I am concerned that the wrong water inflow and outflow and Air Injection, might created. Low DO courners and especially at that back courner, where a stressed. Crush of fish can happen..

I found it interesting to read observations of old timers, that fish deaths are usually always multiple, because of the STRESS created by the first fish death, and I think that I hear this in various post about different systems..

Yes.. we can use IBCs for AP... but there is no way that they are ideal.. courners just don't work well with fluid dynamics..

And. FWIW.. I now have air stones in both back courners of my IBC FTs... at least I can be confident that water is being sucked into this courners, where the fish try to congregate..

The new system, with the round FT, sees fish spread throughout the water volume, as there is no possible hiding place..
(Except when a torch is shone in , and they all try to hide behind the SLO. )
.

Bui Doi,i dont know if you have read this one,this is a paper on Tilapia rearing by Rakocy of the UVI, it clarifies several points on Filtration DO etc.
http://www.thefishsite.com/articles/136 ... f-tilapia/

And thanks for that reference.. also of some interest to the OP..

There is so much material out there, if you have the time to search.. the problem is sifting through the waffle...

One day, someone with a real interest and more importantly CAPACITY.. will determine a suitable rule of thumb for media in a pure Aquaculture system..

I am still interested in finding techniques for controlling Ammonia and Nitrites..
I acknowledge the very valid thought that removing those, will also seriously affect the bacteria culture growth.. but if a spike can be clipped, so as to protect the fish, then this has to be good, whilst leaving sufficient nutrient to maintain bacteria development..
Just another tool, to help with RAS management..
..
.Peter

Speaking of Do BuiDoi, is your airline to the ft garden hose?