Backyard Aquaponics
A place to discuss aquaponics

I understand the ammonia and nitrites can be harmful to fish but are Nitrates harmful? I was thinking that way if you overstocked it would be fine as long as you had good bio filtration. Right?

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What fish and what level of nitrates... that is the question...

Many here have reported levels of way over 100 and no problems

Then, I can say that I had an aquarium that had regular feeds and NO FILTRATION and only top ups for three, and when i did a final reading, all was zero..
As it turns out, deep media and anaerobic bacteria took care of that...
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Studies have shown that most fish species commonly grown in AP can handle short term exposure to Nitrates of about 450+ppm before it starts to affect them. They have also shown that long term exposure to Nitrates as low as 150ppm can also harm them.

If your system is constantly running at 150ppm you have issues anyway, your system is not in balance. At 80ppm most leafy greens start to become bitter. I tell customers if their system constantly runs at anything above 40ppm they need more GB area/plants, or they need to reduce feeding and/or fish numbers.

What is a normal balanced level? and what grows plants best?

There's no way to know what's balanced. As most people don't have a way to test for potassium / phosphorus / Iron / etc. Normal is also relative, some people have Nitrates as high as 100+ and some have 0 with good growth. As long as everything tastes great, grows great, and your fish don't die that's fine.

In order to know your plants can't absorb anymore nitrates you need to have more than 0. But other than that it's just guess work / watching for plant deficiencies.

Anywhere between 0.0ppm to 40ppm...

As Frap mentioned, it's possible to have good plant growth with 0.0ppm of Nitrates if your system is well balanced... many systems run this way.

Most test kits jump from 40ppm to 80ppm and somewhere in between there your greens will start to develop bitterness... at 80ppm there is a definite bitterness to things such as Lettuce, Chard, Asian Greens etc.

Keep it to a max of 40ppm and everything will be fine.

Nitrate levels required by plants are individual to species, as are other elements, micro and macro nutrients. Which usually can be found through a thorough google search derived from farming and hydroponic industries. But adjusting to suit is difficult and timely due to the ecology of aquaponics.

A reading of zero could mean your system is balanced, a reading of zero could also mean you need to up feed ratio or fish stocks. High readings could mean your over stocked, or overfeeding or under plant stocks. The way to determine the mentioned without testing equipment comes with experience.

As MrD mentioned, if you have high nitrates there is a reason and you need to address this. But no need to stress as fish are quite tolerant to nitrates.

Ammonium nitrate can certainly hurt fish! Coming from the US, you may have heard of just how dangerous it can be
http://en.wikipedia.org/wiki/Texas_City_disaster

...but I guess that wasn't the kind of nitrates you were thinking of

Thanks for this - good information

Great info everyone. It just confirms how much I need to drop mine!


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Great info here - my nitrates are heading off scale over the past couple of weeks, today possibly 200 ppm with a rough dilution. Wondering what I should do about it . 19 of my 20 towers are planted and my 2 growbeds are full, but my plant growth has slowed down. I have 25 sassy rainbow trout from 20 to 27 cm long eating around 60-70g of Skrettings a day. My ammonia and nitrites bounce between 0 and 0.25ppm, and pH is constantly dropping so I regularly adjust up to >6.4. I have salted to 1 ppt which is gradually diluting with rainwater topups. Plants look very green and healthy, but today I noticed purplish colour around the centre veins of my hokanwase strawberries - is this phosphous deficiency, and if so, could that be why growth has slowed and they are not keeping up with the nitates?

I use dolomite to adjust pH up (for now), and add a scoop of iron chelates once a fortnight and a cap of seasol alternate fortnights. Thought I might try some lye made from wood ashes to adjust pH and add some P & K and other trace elements. Is this a good or bad idea

What should I do

-keep on going as I have been - don't worry, be happy
- reduce feeding
- get rid of some fish
- add some P to see if the plants crank on
- build some extra GBs under the towers to catch stray leaks and grow more plants
- anything else?

I can load some recent photos tomorrow if required, but you can see my set up on my system thread.

I would stop adding Iron chelate so regularly and only add it every 3 months or so, or when deficiency symptoms first show. I'm only adding Iron to my systems every few months, and only about a 1/4 teaspoon per 500L, especially if using EDDHA.

If you are using a good quality fish food (which Skretting is) and are adding Seasol occasionally, you should very rarely, if ever, need to add extra Iron.

Excess iron will slow, or even stop the uptake of certain elements, Magnesium in particular. Purpling of the leaves is a symptom of Magnesium def' in some plants.

Heading into winter your gross feeding fruiting plants should all be finished by now, so Phosphorus deficiency shouldn't really be an issue, and Potassium deficiency can be easily rectified with the addition of Potassium bicarbonate, which will assist with your pH.

Adding dolomite lime on an ongoing basis and no Potassium may have caused an imbalance in the three way Ca-K-Mg relationship, so using a Potassium bicarbonate may also address that. They should be added at around a 3:1:1 ratio, maybe even a little less of the Mg... After a few months of experimentation I'm actually finding that a 3:1:0.5 (or 6:2:1) ratio is giving me the best results, I'm getting really healthy plant growth.

I'm not 100% certain this will work Joc but try adding a small amount (maybe 1 or 2 Tablespoons roughly 15 to 30 mls mixed in water) of molasses to a grow bed to help with using up the nitrates. It should give some of the bacteria or plants a bit of extra juice for growth and allow them to take in some Nitrate. From Wikipedia - http://en.wikipedia.org/wiki/Nitrogen_assimilation



Adding the sugar will also have an effect on the bacteria in the grow bed (this favors heterotrophs which grow faster than the nitrification bacteria) so we'll see what happens but I think it should help either way just watch your ammonia and nitrite because you might have a bump when some of these die later on (depending on what group gets the carbs).

Let us know what happens if you try this