Backyard Aquaponics
A place to discuss aquaponics

Just went back through the pics,are those your toes ……………..

Ha ha, not you too mate lol, leave the toes out of it haha

Im not good with plant deficiencies., the guys are prob right, it may be magnesium. Ive got a feeling that Nate did a thing on you tube about magnesium recently.



Edit: sorry it was Phosphorus..

Going by the video,my tomatoes are really strong,excellent fruiting and growth. So something else.

Someone mentioned a fungal disease,yellowing leaves with grey spots,the pic shows one..

I use liquid seaweed in my system anytime I see yellowing of leaves. Seems to perk things back up pretty well. It discolors the water but only for about a day. I have had better luck with my peppers now that the weather has cooled down some.

Thanks for that video link Charlie.. now subscribed to Nate's channel

Apart from looking out for plant discoloration etc, do you guys test for phosphorous with a test kit? or not required generally?

Generally not required... despite what Nate says in the video... Phosphorus is/should be the last thing to be deficient in an AP system...

Good to know, thanks Rupe

Phosphorus availability depends from phosphorus input only!
Unless you purchase quality feed or run a water test or you are the God of nutrient deficiency....... I would stick to simple analytical logic and physical analysis.
A simple Phosphorus drips test kit will tell you how much P04 is in your system.
This is the equation or the question you should ask yourself!

How much P is contained in your fish food?
How much fish food are you adding daily?
What stage of growth is your plant?
Do you have fruiting plant?
How much P does your plant need?

Then.....you probably have your answer.

Looking at the Chilli plant in the pic you provided Dasboot, I would confidently say it's not a Potassium or Phosphorous deficiency, nor a fungal infection. Looking at the pattern of the yellowing and the necrotic spots I'm confident you had a Magnesium deficiency, or possibly a viral infection... but if I had to put money it, I'd say Magnesium. Try adding a teaspoon of Epsom salts per 1000L

A few thoughts.. as BAF rightly mentioned before, in Aquaponic systems, the ultimate source of both macro and micro-nutrients is fish food. Deficiencies in fish nutrients usually are of K, Ca, Fe, and P; they must be supplemented. These nutrients can very well be supplemented using natural fish feeds such as Moringa and water hyacinth leaves, and/or Azolla.

Rabbit manure is packed with nitrogen, phosphorus, potassium, and many minerals, lots of micro-nutrients, plus many other beneficial trace elements such as calcium, magnesium, boron, zinc, manganese, sulfur, copper, and cobalt just to name a few. Applying this to fish tank on an as-needed basis would also help.

I may be wrong but this is how I try and add useful nutrients for our plants.

Potassium (K)* - helps in the building of protein, photosynthesis, flowering, fruit quality and reduction of diseases.
Calcium (Ca)* - an essential part of plant cell wall structure and the transport and retention of other elements.
Phosphorus (P)* - an essential part of the process of photosynthesis and in the formation of all oils, sugars and starches.
Iron (Fe)* - essential for formation of chlorophyll.

Looking at your pepper picture, to me it looks like a combination of nutrient deficiency and not a single one. Here is a good reference site worth reading - http://5e.plantphys.net/article.php?ch=t&id=289

It is true Potassium and Calcium may occasionally need supplementing in aquaponic systems, especially when growing a lot of fruiting plants, or heavy feeding greens such as Spinach, Silverbeet etc... but this is usually taken care of with the two most common pH buffering products aquaponics practitioners regularly use... Potassium bicarbonate and Calcium Hydroxide.

Iron deficiency is normally only an issue when the system pH is high, ie: 7.5 or more, and in this case a Chelated Iron product is required due to the high water pH.

Phosphorous deficiency in aquaponics is as rare as rocking horse sh!t... I don't recall reading on this, or other forums I read, of anyone ever actually proving a Phosphorous deficiency in an AP system, but I may be wrong. I have seen a few photo's posted on here where I've actually suspected an excess of Phosphorous may have been the issue.

If you are suggesting all four of the elements you posted above "must" be supplemented on a regular basis as, a matter of course... that is incorrect in my opinion. I know of well established systems where nutrient supplements have never been required, other than some seaweed extract during the initial cycling phase.

The best approach I think is to deal with any deficiency as it appears, firstly by correct identification of the deficiency, secondly with the use of a suitable product to correct the deficiency, thirdly through ongoing preventative measures once you have rectified the initial deficiency.


As are most other animal manures, but from a disease prevention and health & hygiene POV we try and prevent manures from warm blooded animals or certain amphibians entering our AP systems.


What combination of deficiencies would suggest the plant has then Nanniode?...

As a Horticulturalist of 27 years experience and nearly 20 years hydroponic experience, I can tell you with some conviction that I don't believe it's a Calcium, Potassium, Phosphorous, or Iron deficiency!

P.S... FYI


Micro nutrients and Trace elements are one-and-the-same!... and Calcium and Sulphur are neither, they are Macro nutrients.

Thanks Mr. Damage I'm looking at the same problem here and have tried every other deficiency and Magnesium was the next and last option. I've been searching for how to add Magnesium to the system thank you for the advice.

How do you test for Magnesium deficiency? or is it just picked up by poor plant growth?