Backyard Aquaponics
A place to discuss aquaponics

I'm seeing some yellow on the tops of my Tomato plants, PH looks good any other ideas?

lacking iron.

What is your ph reading

I was thinking iron also, PH has been around 6.7 on avg.

Shouldn't be getting an Iron lockout at pH 6.7... or other trace elements for that matter...

But you could cure two birds with one stone... and foliar feed with Maxicrop+Iron...

We touched on this briefly a few days ago, but I'm beginning to form the opinion that a lot of the nutrient deficiencies people are often quoting, especially in relation to tomatoes in established systems... could be caused by excess Phosphorus.

Over the last couple of years I've had a number of people with established systems that have successfully grown tomatoes before, show me tomato leaves, or photo's of leaves with deficiencies. The symptoms have varied across the systems/plants, but looked for all intents and purposes like deficiencies in Potassium, Iron, Magnesium, Calcium and possibly Zinc (can look similar to Magnesium)... some a combination of.

Depending on the symptoms, we have tried all the usual tricks, Chelated Iron, Eco-fungicide, extra Seasol, Epsom salts, Lime, etc, with varied success, some are temporarily fixed, others have had no change and/or the problem has continued to get worse. All the people have commented on how well their tomatoes went in the first season or two, but then they begin to have problems.

I've done a bit of reading up on this in the last few weeks, initially looking into deficiencies of Iron and Magnesium... and the common denominator that continues to come up is excess Phosphorus... which can also affect uptake of Potassium, Calcium, Zinc and copper. Here's a sample of what I keep coming across:Don't get me wrong, I've had customers with straight forward Iron, or Potassium deficiencies that have been solved easily with Chelated Iron and/or Eco-fungicide, but I've had a number where we simply can't solve the deficiency issues and the Tomatoes perform dismally.

Any views on this, or has anyone else had similar issues. I'm just trying to open up discussion on this topic.

Has anyone with an established system and deficiency issues had water analysis done, if so, what were the results?

Seems like a reasonable solution to some of these problems Mr D.

I also would not discount diseases etc.

However, if it is an excess of phosphorous and assuming no phosphorous has been specifically added, it would be interesting to know what the nitrate levels are in such a system? Surely with high phosphorous the nitrates (and other nutrients derived from fish food) must also be very high.
There are some simple phosphorous tests you can buy for aquariums or even get your local pool place to test. I have had some very surprised looks when they have tested my tank water thinking it was from a pool

I currently test for iron and salt 4 times a year (or after a major water change) and will now start looking at further test kits for other elements such as phosphorus.

what levels of phosphorus were considered to cause deficiencies in the other elements?

Leafy greens will suck up just about all the Nitrate you could throw at them, as will fruiting plants in the vegetative phase... so the Nitrates are probably kept in check.

It depends on the ratios of the other elements

In my experience high nitrates are a major problem with levels approaching 800ppm whether I'm feeding 75 silvers in a well planted 5 bed system or 30 trout in a 5 bed system, feeding twice a day as much as they will eat in 5 mins.

Few people test for nitrates and report them on the forum and those that do often get the highest level and assume that is what it is (like I did). I now only feed my silvers 500gm (down from 1kg) per week and my nitrate levels are dropping.

...

yep that what I looked like. Plus a few expletives.
Now I water change and feed less and am begging to be allowed some more grow beds.

BTW my levels are now around 500ppm. I wonder what my phosphate levels are?

While there's a definite inter-relationship between Phosphorus/Calcium/Potassium... and to some extent magnesium... things really have to be way out of whack to invoke other trace element lock outs of zinc, copper, iron etc...

I think we need to be careful extrapolationg things from hydroponic sites.... like the first one when googling...

http://sgsak.com/leaf-spotting/

And nutrient supply websites like... http://www.advancednutrients.com/articl ... ticleID=41

And other hydro sites that are dedicated to the chemistries of growing weed...

Yep... they often do end up chasing their tails with lockouts due to high phosphorus.... because they force the weed flowering with high phosphorus "bloom" formulas...


I really don't believe that high phosphorus levels... or even phosphorus deficiencies... are common place in aquaponics at all...

But...

There could be some correlation in what you're reporting Yabbies...

If you look through the older established system threads.... you see consistant growth.. even tomatoes....

With very few deficiency problems.. or any problems attributable to over-abundance of either phosphorus.. or nitrates...

Why?... because you'll find most of those systems were configured with the (then) accepted 2:1 growing area:fish tank ratio.... and modest stocking levels....

And it makes sense that such systems don't experience such problems... because the (relatively) greater number of plants are utilising the available nitrates and phosphates...

And probably were/are stocking longer term growth fish such as Silver Perch...

With the more recent higher stocking denisties, and simultaneous paring back to more (now) common 1:1 ratios.... that utilisation of nitrate and phosphorus is diminished (relatively)...

And with greater numbers of fish... and the increased predominance of heavy feeding fish ... trout/barra etc... the feed rates/wastes.. in many systems... and corresponding accumulation of phosphorus....

Could indeed be presenting as phosphorus.. or phosphorus inter-dependancy problems...

With the even more recent trend towards soldis waste removal in aquaponics systems... hence removing a large proportion of the phosphorus wastes... from accumulation...

It would be interesting to see whether or not those member systems... suffer the same kind of related problems...

I would suspect.. they wont...