Backyard Aquaponics
A place to discuss aquaponics

System size:
2x 400 gal. fish tanks + around 300 gal. total sump/pump tanks.
100sq ft of media filled beds (plan on adding more to this system)
Its been established for 13 months now. (this is my first system)
Taken some pictures but can't get my old Samsung and my new Windows to play nice tonight.

Have about 60 Tilapia that are a year old, 60 about 5 months. I need to get into a routine of eating a couple every week. If you ask the fish, 2 cups is not enough food !

I've taken out a fair amount of peppers, cukes & toms last fall and through the first part of the winter... So with this and maybe the commercial aquaculture food being reduced in phosphorous got me to where I am?

I'll start with slowly adding some rock phosphate,(per Nate Storey's vids) then maybe over the long run switch out the regular potassium carbonate with the monopotassium phosphate.

Thanks!

Thats amazing that with that feed rate there were almost no phosphorous, shows that the toms and cuc's must have been sucking down hard on the stuff!

I have about 50 sq ft of Growing area in the BYAP systems and have been feeding 40g per day, so little wonder I've experienced nutrient deficiency when heavily planted with fruiting plants.

Makes sense Matty

Heres the environmental data for Spectra FF for trout:

Environmental Impact
Estimated discharge (kg) per 1,000 kg fish produced
Nitrogen (N) FCR = 1.2 FCR = 1.5
Dissolved Waste 47.8 67.2
Solid Waste 8.6 10.8
Total Waste 56.4 78.0
Phosphorus (P) FCR = 1.2 FCR = 1.5
Dissolved Waste 3.6 5.5
Solid Waste 4.1 5.1
Total Waste 7.7 10.7

So for an FCR of 1.2, there is 3.6kg soluble phosphorous for every 1000kg of fish produced. Thats 0.4% of food produces soluble phosphorous roughly speaking, with a bit more in solid waste form - total of about 0.9% phosphorous produced from food. The FF food content of phosphorous is quoted as 0.9% so the fish don't use any.

I originally contacted them to get potassium figures, though they were not forthcoming with that. For Nitrogen the figure is nearly 7% total waste with 6% of it being soluble.

So thats giving a soluble NP ratio of 6:0.4 or 15:1 which seems very high on the nitrogen side seeing as most hydro formulas are around 1:1 or 1:2.

And the K bit at the end is often higher, though is also deficient in fish food!
So I would love to hear what other peoples systems test for for P (and K). Would love to get a lowish cost way of measuring K...

Another thing of interest is when you look at the ratio of solid waste for N:P its 2:1 - a better ratio, I think this goes some way to explaining why mature systems perform better since once the mineralisation kicks in, it starts getting into all that solid phosphorous and potassium that has been stored up in the grow beds - maybe its possible to run the system intensively for 8 months on trout poo then just let it coast the rest of the year on solids with a little bit of supplementation?

Ive read of systems going without fish for some time but every system/situation would be different. Unfortunately when its time to harvest trout -its time to start planting out heavy feeders like tomato's and peppers etc which would consume stocks quickly.

Whilst I was googling around yesterday I came across a statment indication that by the time plants have attained about 25 per cent of their total dry weight, they may have accumulated as much as 75 per cent of their total phosphorus requirements.

We know how PH effects Phosphorus but this little snippet I found this morning was also interesting..

Interesting Charlie, I'm not a full bottle on pH effects on phosphorous. What's the storey with P and pH in aquaponics?

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I was refering to availability to plants at different pH ranges and the effects on other elements. For example, some P forms are absorbed more readily than other forms. Generally P is slightly more available in a pH range of 6.0 to 7.5 pH.

At higher pH levels (>7.5), calcium may react with phosphorus, creating forms that have slightly lower availability to plants. Magnesium acts in the same manner, forming different types of magnesium phosphate compounds.

In more acidic environments (pH <6.0), iron and aluminum increase, which causes either a fixing or removing of P from the solution which limits the availabilty of inorganic P to plants.

A large percentage of new systems run higher pH values which when you look at P availability in alkaline environments, you can only assume a level of deficiency is occuring, to what level we dont know. So that goes in hand with your previous comments in a way. I dont think the acidic example is a problem because we all need to keep pH values above 6.